Police have arrested a 17-year-old boy in south London in connection with last Friday’s terror attack on a Tube train.
The teenager was detained after officers executed a warrant in Thornton Heath at around midnight on Thursday.
It takes the total number of arrests in the investigation to six, all of whom remain in custody at a south London police station.
A homemade bomb partially exploded on a rush hour District Line train at Parsons Green, injuring 30 people.
Police have begun a search of the property where the teenager was arrested under Section 41 of the Terrorism Act.
Commander Dean Haydon, head of Scotland Yard’s 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 six males in custody and searches are continuing at five addresses.
“Detectives are carrying out extensive inquiries to determine the full facts behind the attack.”
Further searches are continuing at two addresses in Surrey and are expected to last some days, the police said.
A search is being carried out by police at an address in Thornton Heath, south London
Three men, aged 25, 30 and 48, have been arrested in Newport, south Wales, a 21-year-old – named as Yahyah Farroukh – was detained in Hounslow, west London, and an 18-year-old man was arrested at the Port of Dover.
The 18-year-old arrested man is thought to have lived in a foster home owned by Ronald and Penelope Jones, in Sunbury-on-Thames, Surrey.
He is thought to have moved to the UK from Iraq aged 15 when his parents died.
The BBC has learnt that he had been referred to an anti-extremist programme before his arrest.
It is not known who made the referral and when, or how serious the concerns were.
A time limit on Mr Farroukh’s detention is expected to expire on Thursday, while detectives have been given until Saturday to continue questioning the 18-year-old.