Two more men have been arrested in connection with the Parsons Green bombing, taking the total to five, Scotland Yard said.
Men aged 30 and 48 were detained during a raid by counter-terrorism officers at a home in Newport, South Wales at around 5.10am this morning.
A third man, 25, who was arrested at a separate address in Newport shortly after 7pm last night, and two other suspects detained on Saturday, remain in custody.
Commander Dean Haydon, head of the Met 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 five 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 cooperation."
The latest raids were carried out by the Met Counter Terrorism Command, assisted by Gwent Police and the Welsh Extremism and Counter Terrorism Unit and both addresses in the town were being searched today.
Detectives had already been granted more time to question two suspects, Yahyah Farroukh, 21, and an 18-year-old man, over Friday morning's bomb attack on a London Underground train, which injured 30.
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: "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 left for the UK in 2013, they said.
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.