British police say they are trying to determine if four men suspected in last week's bombing of London's transport network died in the explosions.

Police say they have made significant progress in the investigation of the bombings that killed more than 50 people and wounded 700 others on three subway trains and a double-decker bus.

The chief of the London police anti-terrorist branch, Peter Clarke, says personal property or documents belonging to three of the four suspected bombers have been recovered at the bomb sites, raising the possibility they are all dead.

"We are trying to establish their movements in the run-up to last week's attacks, and specifically, to establish if they all died in the explosions," he said.

Mr. Clarke said there is a strong amount of forensic evidence that one of the suspects died in a blast on a subway train near the Aldgate station in East London.

Mr. Clarke said closed-circuit television shows all four suspects arrived together by train at London's King's Cross station at around 8:30 in the morning last Thursday, some 20 minutes before the subway blasts.

Police stand guard near a house on Tempest road in Beeston district of Leeds, England after raids throughout area
As the investigation unfolded, police raided a number of residences in and around West Yorkshire county, including the homes of three of the suspects. One man was arrested during those raids.

A police spokesman said authorities were looking for explosives like those used in the London bombings.

British Prime Minister Tony Blair says Islamic terrorists probably carried out the attacks.

But police are stressing that the bombers were terrorists and criminals and there should be no revenge attacks on British Muslims.