British police are searching for a possible mastermind of last week's bombings on the London transit system.
Officials believe four suicide bombers carried out the attacks, which killed at least 52 people.
Police have not officially identified the suspects, but news reports say three were British-born men of Pakistani descent between 19 and 30 years old.
Police, on Wednesday, carried out new searches in the northern city of Leeds, where Tuesday they found what appeared to be a bomb factory and arrested a relative of one of the suspects.
Officials say they believe the bombers had oversight or the assistance of a bomb-making expert who could still be in Britain.
In Brussels, European Union interior ministers today agreed to increase the fight against terrorism, vowing to improve intelligence sharing and police cooperation, and to speed up measures to cut funding for terrorist groups.