Police are continuing to question four people, including a 17-year-old boy, in connection with the Parsons Green terrorist attack.
The teenager was detained after officers raided what neighbours described as a "halfway house" in Thornton Heath, south London, at around 12.05am on Thursday.
The investigation into the rush-hour bombing, which injured 30 people, has also seen two men aged 25 and 30 detained in Newport, south Wales, and an 18-year-old man detained at the Port of Dover.
Two men, a 48-year-old man arrested in Newport on Wednesday, and a 21-year-old man - understood to be Yahyah Farroukh - arrested on Saturday, have been released with no further action, Scotland Yard said.
Warrants for the further detention of the 25-year-old and 30-year-old men were granted until Tuesday, police said.
Searches at an address in Surrey, one in Thornton Heath and two in Newport were continuing.
Officers searching the Thornton Heath property, where the 17-year-old was arrested under section 41 of the Terrorism Act, appeared to be clearing an overgrown garden at the rear of the house with tools including garden shears.
Investigators were seen removing evidence bags from the house and taking items, including a wheelie bin, into a forensic tent erected outside the property before the police cordon was taken down on Thursday afternoon.
Neighbours living near the home, which is beside St Paul's Church and community centre in St Paul's Road, said they believed the property was a halfway house.
Tom McCall, 75, who lives in the house behind the raided property, said police knocked on his door on Wednesday night asking about access to a garage situated between the two houses. Mr McCall said there was some police activity a couple of weeks ago, with police cars parked and officers going in.
Pamela Emanuel, 54, said police visit the house frequently - "at least every other week" - and that the current group of "young foreign teenagers" have lived there for no more than six months. She said she believed the house was used for people with a question mark over their immigration status, and described the group as "unsupervised".
But she added: "They were friendly enough. Quiet. Pleasant enough."
Phil Burt, 67, who has lived at the opposite side of the street for 40 years, said he heard "enormous shouts" at around midnight on Wednesday. He said the shouting, which may or may not have come from police, was so loud that it made at least three dogs in the area bark.
He also said he thought there was some police activity at the house "maybe a month ago".
Paula Anderson, 43, who lives next door to the property and said she was also woken up by "a lot of banging", added: "When I looked out there were lots of police officers."
She said her husband went out and asked the police about what was going on and they told him they were "acting on intelligence". She said she had never had any problems living next door to the house, which she said probably had about seven or eight bedrooms.