The Metropolitan Police has named two of the men it suspects of trying to detonate bombs in the co-ordinated attack on three London Tube trains and a bus last Thursday.
They are 27-year-old Muktar Said Ibraihim and 24-year-old Yasin Hassan Omar.
Police have arrested two more people in connection with the attempted bomb attacks last week.
They have also confirmed that they believe there may have been a fifth bomber, following the discovery of another device in parkland in west London last Saturday
The explosive is reported to be of a similar type to that used in the four unexploded rucksack bombs.
This afternoon, armed police raided another property in London in connection with last week's attempted bomb attacks.
The raid was at a flat in north London, thought to be in the Friern Barnet area, and a search of the premises is ongoing.
Blair apologises for death of Menezes
Meanwhile, the British Prime Minister, Tony Blair, has expressed his sorrow over the death of the Brazilian national who was shot dead by plain-clothes police having been mistaken for a suicide bomber.
Jean Charles de Menezes was shot eight times at Stockwell Tube Station in London last Friday.
Police say they will not abandon their shoot-to-kill policy in the hunt for the suicide bombers.
Senior police officers have been defending the need for police to use deadly force to protect the public from suicide bombers.
Mr Menezes' family says it is thinking of suing the police.
An independent inquiry has opened into the shooting.
