Latest: A bomb disposal team was deployed to a property being searched in Wigan following an arrest linked to the Manchester attack.
What we know so far:
Update 10.40pm: A bomb disposal team was deployed to a property being searched in Wigan following an arrest linked to the Manchester attack.
Police are continuing to guard the terraced house in Springfield Street, which was evacuated on Thursday evening after the discovery of "potentially suspicious items".
Greater Manchester Police (GMP) said officers had been at the address since Wednesday evening, following the arrest of a man said by witnesses to be carrying a suspicious package.
A bomb disposal unit van arrived in Wigan Lane, near to the junction of Springfield Street, at about 7.15pm.
It drove off shortly after 9.05pm and about five minutes later residents in Springfield Street, Bellingham Avenue and Haigh Avenue were told they were now free to return to their homes.
A police cordon, which stretched 100 metres from Springfield Street to the Bellingham Hotel, near to Wigan Infirmary, is expected to be lifted shortly.
Update 9.40pm: British police have reopened information-sharing ties with the US following a spat over leaked evidence from the Manchester bombing, police chiefs said.
Mark Rowley, the country's most senior counter-terrorism officer, confirmed they had "received fresh assurances" from their foreign counterparts and were now "working closely" with them.
An extraordinary row erupted between the US and British authorities after a host of sensitive information was leaked to American news outlets in the wake of Monday's attack.
Mr Rowley said: "We greatly value the crucial relationship with our trusted partners around the world so we can collaborate and share sensitive information to defeat terrorism and protect the public at home and abroad.
"While we do not usually comment on information-sharing arrangements with international law enforcement organisations, we want to emphasise that, having received fresh assurances, we are now working closely with our key partners around the world including all those in the Five Eyes intelligence alliance."
Apparent leaks from the investigation, including evidence photographs from the scene of the attack, were said to have caused "distress and upset" to victims' families.
Home Secretary Amber Rudd publicly rebuked the US authorities for passing on the information unauthorised, only for more material to surface in the New York Times hours later.
The Prime Minister said she would raise the leaks with President Donald Trump in the margins of a Nato summit in Brussels, stressing that the "special relationship" was based on trust.
President Trump vowed to investigate, calling the leaks "deeply troubling" and warning the sources of the security lapse could be prosecuted.
Update 8.07pm: A street has been sealed off as police continue to search a property in Wigan amid reports that a bomb disposal unit was called to the scene.
Eyewitnesses posted photos on Twitter showing a bomb disposal van, and at least one street sealed off with a police cordon while a helicopter circled above.
Greater Manchester Police said officers had been at an address in the area since Wednesday evening, following the arrest of a man carrying a suspicious package.
A helicopter circled above the cordoned-off area, which stretched on to Wigan Lane, near the Wigan Royal Infirmary, while emergency vehicles filled the road, one witness said.
Wigan Council said Wigan Lane was closed between Mesnes Road and Central Parkway due to "a police incident", warning the public to avoid the area.
Update 6.41pm: Manchester bomber Salman Abedi phoned his mother hours before his attack and said "forgive me", a Libyan anti-terror official has said.
Update 6.33pm: 27 major trauma centres in England have been told to prepare staff for a potential terrorist attack ahead of the Bank Holiday weekend.
NHS England has advised them to make sure employees are familiar with major incident plans.
Meanwhile, surgical staff have been advised to review how they deal with patients suffering blast and ballistic injuries.
Update 5.40pm: Manchester bomber Salman Abedi was known to the security services and his risk to the public remained "subject to review" before carrying out his deadly attack.
Abedi, whose sister said he "wanted revenge" for Western military strikes in the Middle East, was a "former subject of interest" to MI5, a Whitehall source confirmed.
Details of the intelligence agencies' knowledge of Abedi came as police hunting the network behind his attack said they had made "significant" arrests and seized "very important" items in raids linked to the investigation.
After chairing a meeting of the Cobra emergency committee, Theresa May said the terror threat level will remain at critical - meaning another attack is expected imminently.
In an indication of the level of counter-terrorism activity, a senior Whitehall source revealed that 18 plots had been foiled since 2013 in Britain.
Those included five since the Westminster attack in March this year.
It is understood the scale of the threat being dealt with by counter-terror agencies is on an "unprecedented" scale and intelligence officers faced "difficult professional judgments" about where to focus their investigations.
The source said: "MI5 is managing around 500 active investigations, involving some 3,000 subjects of interest (SOIs) at any one time.
"Abedi was one of a larger pool of former SOIs whose risk remained subject to review by MI5 and its partners.
"Where former SOIs show sufficient risk of re-engaging in terrorism, MI5 can consider reopening the investigation, but this process inevitably relies on difficult professional judgments based on partial information."
Eight people remained in custody in connection with Monday's attack, in which Abedi targeted music fans at an Ariana Grande concert at Manchester Arena, killing 22 and injuring dozens.
Greater Manchester Police Chief Constable Ian Hopkins said: "I want to reassure people that the arrests that we have made are significant, and initial searches of premises have revealed items that we believe are very important to the investigation."
The killer's sister, Jomana Abedi, told the Wall Street Journal her brother may have been reacting to US-led strikes in the Middle East.
"I think he saw children - Muslim children - dying everywhere, and wanted revenge," she said.
"He saw the explosives America drops on children in Syria, and he wanted revenge. Whether he got that is between him and God."
The British-born son of Libyan parents, Abedi had been banned from a mosque in Manchester after criticising an imam for "talking bollocks" during a sermon critical of the Islamic State (IS) terror group and the authorities had been warned about concerns he was developing radical views.
The 22-year-old's father Ramadan and brother Hashim have been detained in Libya and another brother, Ismail, was arrested in Manchester on Tuesday.
Meanwhile UK frustration at repeated leaks of sensitive information by US agencies led to the suspension of co-operation between the police and law enforcement counterparts across the Atlantic.
Mr Hopkins said the leaks - including leaked evidence photographs from the scene of the attack published by the New York Times - had caused "distress and upset" to the victims' families.
Defending its decision to publish the pictures the New York Times said: "The images and information presented were neither graphic nor disrespectful of victims, and consistent with the common line of reporting on weapons used in horrific crimes."
The Prime Minister said she would raise the leaks with US President Donald Trump in the margins of a Nato summit in Brussels, stressing that the "special relationship" was based on trust.
She said: "Part of that trust is knowing that intelligence can be shared confidently and I will be making clear to President Trump today that intelligence that is shared between law enforcement agencies must remain secure."
The president criticised the leaks and vowed to investigate.
In White House statement, he said: "The alleged leaks coming out of government agencies are deeply troubling. These leaks have been going on for a long time and my Administration will get to the bottom of this. The leaks of sensitive information pose a grave threat to our national security.
"I am asking the Department of Justice and other relevant agencies to launch a complete review of this matter, and if appropriate, the culprit should be prosecuted to the fullest extent of the law.
"There is no relationship we cherish more than the Special Relationship between the United States and the United Kingdom."
Home Secretary Amber Rudd said she was "confident" the leaks would stop and the suspension of intelligence-sharing would be temporary.
The US acting ambassador to the UK Lewis Lukens said Washington was "determined" to stop the leaks of information.
The Queen visited some of the youngsters injured in the blast at Royal Manchester Children's Hospital and condemned the "very wicked" attack.
Prof Bob Pearson, medical director of Central Manchester University Hospitals NHS Trust, said 18 adults and 14 children injured in the blast remained in hospital.
They included five adults and five children who were in critical care, he added.
They were among the 75 people admitted across eight hospitals in the region, including 23 in critical care.
The monarch's visit came after the nation fell silent at 11am to mark the atrocity.
Crowds gathered at well-known sites in the UK, including London's Parliament and Trafalgar Squares, and Manchester's Albert Square.
Police are searching a house in Wigan after a man was arrested in the town on Wednesday as part of the investigation into the Manchester bombing.
A Greater Manchester Police spokesman said: "We made an arrest in Wigan yesterday in connection with the investigation into the horrific incident at Manchester Arena.
"Following this arrest, a house in Wigan was raided this morning and is currently being searched."
A bomb disposal squad was called to a property in Withington on Thursday after a man was arrested on Wednesday night, police said.
Police also confirmed they were searching a property in Moss Side following an arrest on Wednesday.
Update 4.23pm: Armed police officers are patrolling on board trains nationwide for the first time.
British Transport Police (BTP) announced the measure in a bid to "disrupt and deter criminal activity" on the rail network after the UK terror threat level rose to critical in the wake of the Manchester attack.
Armed officers have been patrolling on the London Underground network since December, but this is the first time they will travel on trains outside the capital.
BTP Chief Constable Paul Crowther said the deployment of armed officers will be focused on rail routes serving "big city locations" but will not be limited to those.
"The aim is for it to be unpredictable and widespread across the network, to create a deterrent and an immediate response to terrorists who may be thinking of (attacking) the transport network," he told the Press Association.
Among the first to be deployed were a group of four officers who boarded a Virgin Trains service at London Euston travelling to Birmingham New Street shortly after 2pm on Thursday.
Mr Crowther went on: "Since the devastating events in Manchester on Monday evening, our force has radically increased the presence of our officers nationwide.
"By having firearms officers on board trains we're ensuring that trains remain as safe as possible for passengers.
"Our patrols will be highly visible and passengers should feel comforted by their presence."
Mr Crowther urged passengers not to be alarmed by the presence of armed officers.
"These are normal officers," he said. "They are very approachable. They are there to engage with people, to talk to them about any concerns they've got. I'd really encourage people to approach them."
Since the Government activated Operation Temperer, BTP has benefited from additional firearms officers from the Ministry of Defence Police, who will remain at stations in London.
Mr Crowther insisted that BTP does not have any specific intelligence in relation to a threat to the rail network, but called for the public to remain vigilant.
He said: "In light of the dreadful events over these last few days, and the increase to the national threat level, nothing should be considered too trivial to report and any information - regardless of whether you feel it is significant or not - may be important to all of us.
"The cowardly acts of terrorists will never weaken our resolve."
Paul Plummer, chief executive of the Rail Delivery Group, representing train operators and Network Rail, said: "It is absolutely right that the British Transport Police takes all necessary steps to keep the travelling public and visitors to stations safe.
"Together with the police, everyone on the railway will be remaining vigilant."
Manchester Victoria station, which is attached to Manchester Arena where the blast happened, was closed to allow a forensic search of the area and has not yet reopened.
Update 4.09pm: Counter-terrorism officers have swooped on an address in Warwickshire, thought to be connected to the Manchester Arena suicide bomb attack investigation.
The property in Nuneaton, home to a Libyan-born man who fled the Gaddafi regime, is being searched following an arrest on Wednesday.
An eight-strong police specialist search team, equipped with a ladder, and other officers were seen entering a semi-detached home in Earls Road on Thursday.
Two marked police vans were parked in the street and there was continued activity at the house through the morning.
Officers had been carrying out high-visibility patrols in the area throughout the night.
Neighbours confirmed that a father-of-five named Naser Elshetwi lived at the address, who earlier this year spoke of how he had been shot in Libya in a violent kidnap attempt.
The man, who was in Libya to build a petrol station for a family member, told a UK newspaper how he had been left disabled and struggling to walk, after being shot through both legs in January 2016.
Speaking to the Coventry Telegraph in May this year, and pictured with a leg brace, he said: "My hope is that I will eventually be able to work again, to support my family, but I know that I am lucky to be alive."
The identity of the arrested man is not known.
The newspaper reported Libyan-born Mr Elshetwi came to the UK two decades ago, and was later granted British citizenship under then-home secretary David Blunkett.
He has five children aged between seven and 21 years old.
In a statement last night, Greater Manchester Police said: "This evening we have been carrying out searches at an address in Nuneaton, Warwickshire, and have arrested a man.
"These searches are connected to Monday's attack on Manchester Arena, but this is a fast-moving investigation and we are keeping an open mind at this stage."
Witness Susan Wild said armed officers, with their faces covered, were seen outside the property at about 9.10pm on Wednesday.
"I was just putting my rubbish out and they swarmed the area," the 40-year-old said. "They were shouting 'armed police' and there was about 12 of them.
"The police have been there all night and they've taken plastic boxes in there.
"I would say the family have lived there at least 11 years, which is as long as I have lived here."
Another neighbour, who asked not to be named, said: "I speak as I find - they are just a normal family. I do know them and all I could say about them is good things."
The man was arrested by West Midlands Counter Terrorism Unit and Warwickshire Police officers and is believed to have been transferred to a police station in the Greater Manchester area.
Armed police detained a suspect on a grassed area near flats in nearby Meadow Street, Nuneaton.
One resident estimated that the arrest operation - with armed officers standing over a man dressed in dark clothing - took up to 30 minutes after beginning at about 8.30pm.
Lee Paget, whose flat overlooks the scene, said: "I was in the bedroom and I saw two police come over the road with guns and a Taser.
"The lad was on the floor and there were officers blocking the road off with cars. He just lay there and they had guns with green lasers pointed at him.
"Then the police went to the boot of a car and got out boiler suits and put them on. They took their time."
According to witnesses, officers then placed see-through plastic bags on the man's hands and feet and then asked him to step into a protective forensic suit.
A woman who also saw the arrest added: "They asked him about a mobile phone and they turned around and took that.
"They then said 'We're going to get you up' and we want you to put your feet in these bags.
"They put him in a white hooded outfit like a forensic-type suit and then took him away."
Update 3pm: The publication of leaked evidence photographs from the scene of the Manchester terror attack was "neither graphic nor disrespectful of victims", the New York Times has said.
Images, suspected to have been sent to the paper by US police officials, caused outrage when they surfaced on Wednesday and led to a spat between the country and British authorities.
The New York Times said in a statement: "The images and information presented were neither graphic nor disrespectful of victims, and consistent with the common line of reporting on weapons used in horrific crimes.
"We have strict guidelines on how and in what ways we cover sensitive stories. Our coverage of Monday's horrific attack has been both comprehensive and responsible."
Among the material released were images of the bomb's detonator, the attacker's tattered backpack and remnants of the blast's shrapnel.
It proved a further headache for British security circles and came hours after Home Secretary Amber Rudd publicly rebuked US authorities for unauthorised leaks.
Following the publication of the New York Times's story, Greater Manchester Police temporarily severed information-sharing ties with their American counterparts.
A furious response from counter-terror chiefs was also issued after the story was released, saying such releases "undermine our investigations".
Update 12.35pm: Salman Abedi was reported to authorities for his extremist views after criticising an imam for "talking bollocks" during a sermon criticising the Islamic State (IS) terror group.
A number of people who knew him, and even family members, had reportedly warned authorities he was developing radical views - including, the BBC said, that being a suicide bomber was ok - prompting concerns that signs of the threat he posed were missed.
The 22-year-old’s father Ramadan and brother Hashim have been detained in Libya and another brother, Ismail, was arrested in Manchester on Tuesday.
In an interview before his arrest Ramadan Abedi rejected claims he was a member of the Libyan Islamic Fighting Group, but added that he supports the organisation, which is banned in the UK.
In the translated interview, shown on BBC, he said: "I condemn anyone who says I belong to Libyan Islamic Fighting Group.
"I commend them but I don’t belong to any organisation."
Update 12pm: Her Majesty, the Queen of England, has visited a children’s hospital in Manchester.
Update 11.45pm: A suspicious package which prompted an alert in Hulme has been deemed safe, Greater Manchester Police said.
An army bomb disposal team was sent to the scene and several roads were closed, including Linby Street and Jackson Street.
But GMP later said the incident "has now been deemed safe and the cordon has been removed".
UPDATE - This incident has now been deemed safe and the cordon has been removed. Apologies for any confusion. pic.twitter.com/xdE9jqODeN— Greater Manchester Police (@gmpolice) May 25, 2017
Update 11am: A minute’s silence is being held across the UK to remember the victims of Monday’s Manchester attack.
8 men are now being questioned over the bombing which claimed the lives of 22 victims - mostly women and children.
20 of the 64 injured are said to be critical.
Update 6.30am: Two men have been arrested by counter-terror police in Greater Manchester in connection with Monday’s attack, bringing the number in UK custody to eight.
One of the men was detained following searches of an address in the Withington area of the city, while another was arrested in a part of Greater Manchester that was not disclosed.
A woman arrested in the Blackley area of Manchester on Wednesday has been released without charge.
Earlier: Counter-terror police have carried out a controlled explosion as they searched a property in the Moss Side area of Manchester in connection with Monday’s attack.
Locals reported hearing a "loud bang" in the area south of the city centre at around 1.45am on Thursday.
Six men are in custody following a series of raids across Manchester, Wigan and Nuneaton, Warwickshire, following the attack by bomber Salman Abedi that claimed 22 lives.
A woman who was arrested in the Blackley area of Manchester on Wednesday has been released without charge.
Greater Manchester Police confirmed another search of an address had taken place, although there were no reports of any further arrests.
The force said in a statement: "This morning we have been carrying out searches at an address in the Moss Side area during which a controlled explosion took place.
"These searches are connected to Monday’s attack on the Manchester Arena, but this is a fast, ongoing investigation and we are keeping an open mind at this stage.
"As it stands, six men and one woman have been arrested in conjunction with the investigation and remain in custody for questioning."
The explosion was heard in the neighbouring areas of Rusholme and Fallowfield, with concerned locals taking to social media.
One wrote: "Does anyone know if the loud bang heard at 1:45amish this morning in/near Moss Side & Rusholme was an un/controlled explosion?"