Clarke told the BBC the attacks mean people must stand up against the kind of extremism that can lead "four young men to blow themselves and others up" in London.
Police on 12 July identified four suspects and said it is very likely at least one of them died in the attacks on London's transport system.
British media have gone further, saying all four attacks were the work of suicide bombers and naming three of the suspects as young British-born men of Pakistani origin.
Police said one man was arrested on 12 July in connection with the attacks, which killed at least 52 people.
Hunt Goes On For Clues In London Bombings
British Muslims Condemn London Attacks, But Fear Intimidation