Detectives investigating an explosion on a London Underground train which sent passengers and those in the vicinity fleeing in fear have made their first arrest.
Here is what we know about the incident so far: An 18-year-old is in police custody having been detained on suspicion of being a terrorist by Kent Police in Dover - the arrest was described as "significant" by Deputy Assistant Commissioner Neil Basu. Home Secretary Amber Rudd said the arrest was "very significant", but added: "The operation is ongoing." An armed police operation is under way by counter-terror officers investigating the Parsons Green bombing, with residents in the Cavendish Road area of Sunbury-on-Thames, Surrey, told to leave their properties. Scotland Yard said it has spoken to 45 witnesses, while 77 images and videos have been sent to detectives by members of the public. The national threat level remains at "critical" - the most severe rating - having been raised in the wake of Friday's blast. It means a terror attack "may be imminent". Metropolitan Police Commissioner Cressida Dick said the threat "does not by any means necessarily mean that people have to get used - in fact God forbid that they should get used - to repeated attacks". Troops have been dispatched to key sites across the country to free up armed police officers, with promises of "enhanced police presence" on the transport network. Three patients remain in hospital, with 27 of the 30 injured having been discharged, according to NHS England. Police said most of those hurt were suffering from "flash burns". Parsons Green station has reopened after the explosion was carried out towards the rear of a District Line train, bound for central London, at 8.20am on Friday. Scotland Yard and the Prime Minister have rebuked US President Donald Trump over his claim the Parsons Green Tube bomber was "in the sights" of Scotland Yard. Assistant Commissioner Mark Rowley said police were "chasing down suspects". The Islamic State (IS) terror group has claimed responsibility for the attack through its Amaq news agency, according to the US-based Site Intelligence.