A third man has been arrested in connection with the Parsons Green terror attack, Scotland Yard said.
The 25-year-old was held in a counter-terrorism raid in Newport, South Wales, shortly after 7pm on Tuesday.
Witnesses to the arrest described officers "jumping" a man who was put into a police car and driven away.
Nearby resident Sully Ali, 19, a part-time model, told the Press Association: "A big van pulled up and six officers got out and jumped this guy.
"There were two armed officers there, they didn't have their guns pointed at him but they had them on show.
"The guy was smiling. I didn't hear him saying anything or the police saying anything to him."
Mr Ali said the arrested man worked as a painter and decorator for some local residents.
He added: "They were Met Police officers - they were wearing hats saying Met Police and they didn't speak like anyone from round here.
"He was arrested and handcuffed by officers wearing suits.
"They handcuffed him and led him away, they didn't put him in the van though - they put him in a marked police car."
Two other suspects - Yahyah Farroukh, 21, and an 18-year-old man - remain in custody after detectives were granted more time to question them over Friday morning's bomb attack on a London Underground train.
Residents said the arrested man had lived in the area for many years and attended local mosques.
"He was a nice guy, everybody knew him," one man said.
"He was a student here and he worked as a painter and decorator."
One mother added: "He did some painting on our house about two years ago.
"He was a nice guy, he was very softly spoken.
"He used to condemn terrorism in front of my husband, my husband would condemn terrorism and he would agree with him.
"I know he is a Muslim but I don't know what mosque he went to. Muslims in this area are totally shocked, we condemn terrorism totally and we totally condemn what happened in London."
The raid was carried out by the Metropolitan Police Counter Terrorism Command, assisted by Gwent Police and the Welsh Extremism and Counter Terrorism Unit (WECTU) and an address in the town was being searched on Tuesday night.
Commander Dean Haydon, head of the Counter Terrorism Command, said: "This continues to be a fast-moving investigation. A significant amount of activity has taken place since the attack on Friday.
"We now have three men in custody and searches are continuing at four addresses. Detectives are carrying out extensive inquiries to determine the full facts behind the attack.
"We anticipate that the searches will take some days to complete and may cause further disruption.
"However it is important that we continue with these searches and I'd like to thank all those affected for their support, patience and co-operation."
The family of the second suspect questioned over the Parsons Green bombing earlier insisted he was innocent and "loves the UK", according to reports.
The older man's family expressed their shock after the Syrian refugee was arrested on Saturday night as he finished a shift at a fried chicken takeaway.
His brother Hamed told the MailOnline from Egypt that Farroukh did not mix with extremists.
He said: "He is a good guy. He works in a restaurant to make a living. He would not hurt anyone.
"My father, God bless his soul, brought us up to live decently and with high morals. Yahyah has never mingled with bad guys or militants or Daesh people."
The family said they left Damascus, in war-torn Syria, in 2012 and moved to Egypt, where their sick father died recently.
Farroukh had travelled to the Netherlands to visit them during the Muslim holy period of Eid, shortly after the death, they said.
Scotland Yard said magistrates had granted warrants allowing the 18-year-old to be held until Saturday, and Farroukh until Thursday.
The news came as fresh CCTV footage emerged that appears to show the Parsons Green bomb suspect on his way to plant his home-made device.
The video, obtained by the Press Association, shows a figure dressed in grey carrying a distinctive white Lidl carrier bag around 80 minutes before the explosion that injured 29 people.
Both Farroukh and the younger man, understood to be the suspected bomber, are believed to have spent time in foster care with Penelope and Ronald Jones, aged 71 and 88 respectively, who previously received MBEs for services to children and families.