British police have identified four men who allegedly carried out last week's deadly bombings in London and arrested another suspect after a series of raids in northern England, officials said Tuesday.

At least two of the bombers were apparently killed in the blasts Thursday, and investigators are trying to determine whether all four died in what increasingly appear to have been suicide bombings, authorities said.

In a news briefing on the fast-moving investigation into the bombings, police said surveillance cameras showed the four suspected bombers -- all residents of the West Yorkshire area of northern England -- arriving at the King's Cross train station in London shortly before 8:30 a.m. on July 7. Three took the train from the city of Leeds, and the fourth apparently boarded at Luton about 30 miles north of the British capital.

Peter Clarke, head of the anti-terrorist branch of Scotland Yard, told the briefing that investigators are working to trace the men's movements and specifically to "establish if they all died in the explosions."

He said investigators have found personal documents bearing the names of three of the men close to the seats of three of last week's explosions. Clarke said property belonging to a man who has been reported missing by his family was found on a double-decker bus that was blown up, and that it was "very likely" that one of the men from West Yorkshire died in one of three explosions on subway trains.

Clarke said one man was arrested Tuesday morning in connection with a series of raids in Leeds and will be brought to London for questioning. No further information on the arrested man was immediately released.

The break in the investigation came after investigators found property of one of the alleged bombers in the wreckage of the London bus.

Acting on the information, security forces raided at least six homes in Leeds and closed a railway station Tuesday as part of the massive probe into last week's London bombings.

A bomb disposal unit of the British Army set off what officials described as a controlled explosion at one of the Leeds homes, apparently to destroy material that police suspected to be explosives. Police entered the unoccupied house in a search for explosives and other evidence, authorities said. As many as 600 people were evacuated from the neighborhood of row houses in the city 185 miles north of London.

Witnesses reported seeing at least one person being taken away in connection with the raids.

Two British broadcasting networks reported that the bomber responsible for the bus attack -- one of four deadly bombings targeting London's transportation system -- was apparently among 13 people who were killed in that explosion. Sky News and the British Broadcasting Corp. reported that police identified the bomber and that this information led to the raids in Leeds.

The BBC later quoted police sources as saying that all four suspected bombers were British citizens of Pakistani origin. There was no immediate official confirmation from authorities, but police cautioned people against retaliating against any ethnic group.

At least 52 people were killed in the four bombings, three of which were carried out on subway trains. More than 700 people were injured in the blasts, and 56 were still in hospitals Tuesday, news agencies reported.

So far, however, only five of the dead have been formally identified, and authorities have released the names of only three of them. Faced with mounting public frustration over the slow pace of the identification process, the government pleaded for patience, emphasizing the horrific nature of the bombing scenes and the difficulties of identifying bodies that have been blown apart or disfigured.

In addition to the raids in Leeds, police closed down the Luton railway station as part of an operation to recover a car that was believed to have been used by one of the bombers. Streets surrounding the station were cordoned off as authorities examined the vehicle in a parking lot.

The raids in Leeds began about 6:30 a.m. local time as police searched five homes under anti-terrorism warrants.

About five hours later, the army's bomb disposal unit set off the controlled explosion so that anti-terrorist officers and local police could continue searching a sixth house.

Besides evacuating area residents, police cleared people from a nearby mosque, a health center and a home for the elderly.

Police Inspector Miles Himsworth said detectives were searching for explosives and other items, possibly including computers, the Associated Press reported.

"It's a very, very complicated investigation," Himsworth said, according to AP. "It will be a very slow and very meticulous search. . . ."

In the news briefing in London, Andy Hayman, assistant commissioner of Scotland Yard, said that from the beginning, "we have worked painstakingly to put together every shred of evidence that we could to mount . . . a successful investigation." He said several hundred witnesses have been interviewed, more than 2,000 "very useful and constructive calls" have come in to an anti-terrorism hotline and about 2,500 closed-circuit surveillance tapes have been obtained and are being "urgently viewed."

Clarke said the homes of three of the four suspected bombers were among those searched Tuesday.

He said unspecified personal property belonging to three of the men was found at three bombing sites. He indicated that remains of a bomber may have been found at the site of one of the subway blasts, at Aldgate, but said this was subject to confirmation by a coroner.

Hayman urged Britons not to target any minority group for the bombings, saying the attacks were the work of "terrorists and criminals" and should not be used to "smear or stigmatize any community."

Branigin reported from Washington.