Homes are being searched, and details have been released about the suspects.
LEEDS, England (AP) -- Police pursued what they suspect is a mastermind behind London's terror attacks, raiding a home Wednesday and widening their search to a new area. The top law enforcement official suggested the bombers were "foot soldiers."
Wednesday night's raid in Aylesbury, some 40 miles northwest of London and near the city of Oxford, resulted in no arrests, but police were searching the house, Scotland Yard said.
As a show of defiance, London's trademark black taxis and red double-decker buses were asked to pull to the side of the road and workers were urged to take to the streets at midday today for a moment of silence marking the week that has passed since the July 7 terrorist bombings killed at least 52 people.
Details emerged Wednesday about the lives of the four suspected bombers, one of whom was only 19 years old. Another had gone to Pakistan for two months this year to study religion. At least three of the suspects were Britons of Pakistani descent.
"These foot soldiers who have done this are only one element of an organization that is bringing about this kind of mayhem in our society," Home Secretary Charles Clarke, the country's top law enforcement official, told the British Broadcasting Corp. "We are looking very, very closely at the relationship between the people who may have committed the offenses and the wider network around them."
Clarke said nations needed to defend their values "against those who would destroy it."
"That means standing out against, in a very strong way, anybody who preaches the kind of fundamentalism, as I say, which can lead four young men to blow themselves and others up on the tube on a Thursday morning," he said.
His comments went beyond the cautious statements of police, who said Tuesday that they were investigating the possibility that all four suspects died in explosions on a bus and three subway trains.
The Home Office said there was no evidence at this point to support a conclusion that the bombers intended to die.
Searching for meaning
Several officials, including Foreign Minister Jack Straw, have said the attacks bore the "hallmark" of Al-Qaida. Two claims of responsibility purportedly from militant Islamic groups have surfaced.
A U.S. government official confirmed Wednesday that Shahzad Tanweer, Hasib Hussain and Mohammed Sidique Khan are thought to have been three of the bombers. The names are being checked to see if they appear on any U.S. databases. The official spoke on condition of anonymity because British investigators have not publicly released the identities of the suspected attackers.
Britain's Press Association, citing police officials, said Wednesday that police had identified the fourth suspected bomber but no name or details were reported.
Surveillance cameras captured the four as they arrived in the capital 20 minutes before the beginning of the rush-hour explosions.
Police refused to comment on a BBC report that authorities were seeking a fifth suspect.
In London, police continued to search through voluminous evidence from closed-circuit TV footage and the grisly scene where the blasts ripped apart three trains and a bus. In and around the northern city of Leeds, home to a large Muslim community, police searched for evidence in sealed-off neighborhoods where three of the four suspects lived.
More than 100 possible revenge attacks -- including the killing of a Pakistani immigrant -- have been reported in Britain since the bombings. Police increased protection in Muslim communities.
"This is not an isolated criminal act we are dealing with," Prime Minister Tony Blair told Parliament. "It is an extreme and evil ideology whose roots lie in a perverted and poisonous misinterpretation of the religion of Islam."
Blair said the government also would look urgently at how to strengthen the process for excluding from Britain those who incite hatred and make it easier to deport such people.
In a series of police raids on six homes in the Leeds area on Tuesday, police hunted for explosives and computer files that could lead to a mastermind behind the London attacks. They arrested a 29-year-old man identified by Press Association as a relative of one of the suspected bombers. On Wednesday, a judge approved a warrant for police to keep the unidentified man in custody through Saturday.
One of the alleged bombers, Shahzad Tanweer, was a 22-year-old cricket-loving sports science graduate; Hasib Hussain was 19; and Mohammed Sidique Khan was the 30-year-old father of an 8-month-old baby.
Tanweer's uncle, Bashir Ahmed, said his nephew had gone to Pakistan for two months earlier this year to study religion, and that the family believed he was attending "some religious function" on the day of the bombings.
"It was total shock, I mean, it's unbelievable," Ahmed told reporters.
"Our lives have been shattered," he said. "It's impossible to describe it. We have had a very pleasant time here. I don't think we can continue here."
Neighbors of Tanweer in Leeds' rows of Victorian-era red brick houses were apprehensive and hostile, walking quickly past reporters gathered at the cordons. One warehouse worker, who would only give his first name, Saj, said Tanweer was a "good lad" and athlete.
"He was quiet," he said. "He was religious. He went to every mosque here. There are loads of mosques here."