A third man has been arrested by police investigating the attempted bombings in London on 21 July.
Police said he is being held under the Terrorism Act in Tulse Hill, south London.
Meanwhile, police are continuing to question two men arrested in Stockwell in connection with Thursday's aborted bomb attacks.
The Commissioner of London's Metropolitan Police, Sir Ian Blair, earlier said there is no reason to believe last week's would-be bombers have left Britain.
Straw defends shoot-to-kill policy
British Foreign Secretary, Jack Straw, has defended the police shoot-to-kill policy in relation to terrorists.
He maintains there is no alternative when tackling suspected suicide bombers.
Mr Straw expressed his deep regret about the killing of 27-year-old Jean Charles de Menezes who was mistakenly shot by police during an anti-terrorist operation on Friday.
Brazil's Foreign Minister, Celso Amorim, sought an explanation for the killing on a visit to London today.
Mr Straw spoke by phone to Mr Amorim and assured him there would be an inquiry into the killing.
As the hunt for those responsible continues, the families of the victims of the London suicide bombings have been visiting the four locations where their loved ones died on 7 July.
52 people were killed in the explosions at Aldgate, Edgware Road and Russell Square underground stations and on a bus at Tavistock Square.
The Aldgate and Edgware Road underground stations were open for flowers and other tributes to be left.
But continuing recovery work on the wrecked train near Russell Square meant family members there had to pay their respects above ground.
