British authorities said they were hunting Wednesday for the masterminds of last week's bombings in London amid shock over the news that the attacks were apparently carried out by four Islamic extremist suicide bombers born and bred in Britain.

British newspapers said the four who carried out the bombings last Thursday that killed at least 52 people on three subway trains and a bus in London were all Britons of Pakistani origin.

All the reports, which cited a variety of intelligence and police sources, said the bombers traveled to London together by commuter train from Luton, a town just north of the capital. After a brief and undemonstrative goodbye, they separated at King's Cross station in the center of the British capital before launching their attacks in Thursday morning's rush hour.

The identities of the suspected bombers, aged between 19 and 30 years old, emerged after the police raids in Leeds on Tuesday.

The suspects were named in newspaper accounts as Shehzad Tanweer, 22, Hasib Mir Hussain, 19, Mohammed Sadique Khan, 30, and Eliaz Fiaz, 30.

Some personal details were given such as that Tanweer was a science major from Leeds University, while Khan was a married father of a baby girl who worked with handicapped children.

The Evening Standard said Hussain was to have bombed another subway line but the line had been suspended that day. He then panicked and ended up setting off the bomb on the bus.

His driving permit and other personal effects were reported found in the remains of the bus.

Police gained vital clues from Hussain's parents, who knew their son was in London and were unable to contact him by phone once the bombs went off, The Times said.

None of the four were on the files of security services, papers said, making them so-called "cleanskins," terrorists with no previously known link to suspicious groups and thus incredibly hard to track down before they strike.

Police however have yet to say explicitly that all four attacks were carried out by suicide bombers.

Searching for masterminds

BBC television, quoting senior security sources, reported that the police were searching for a fifth suspect who may have been their "controller" or the bombmaker.

In an interview with BBC Radio, British Home Secretary Charles Clarke said "we have to attack the people who are driving, organizing and manipulating those people" who carried out the bombings in the British capital.´"And that's of course where the police investigation is going just at this moment," Clarke said.

He said he did not know "what was the nature of the relationship of these four people to people more widely," without ruling out government suspicions that they were linked to or inspired by Osama bin Laden's al Qaeda organization.

He also said that the British authorities had to address
"international links" to the bombings and to "organize ourselves on the basis there are other people prepared to act in this way."

Unsettling realization

The revelation that the bombers might be born-and-bred Britons sparked a bout of national soul-searching in the press.

"Suicide bombers from suburbia," read the banner headline in the Daily Mail above a photograph of police vans standing on a street of ordinary-looking terraced houses in the northern English city of Leeds, where police raided several homes on Tuesday.

"The conclusion that the terrorists were home-grown is deeply unsettling. It does not, in any way, close this case," The Times said in an editorial. "Is it really possible that no one beyond the bombers had any inkling of their intentions?" it asked.

The Guardian, for its part, described news that the bombers were British as "the worst of all possible outcomes. ... It will have been the work of people brought up in our multi-racial society of which policy-makers were rightly proud. This is not just a challenge for government but for civic society, too."

The bombs on the London Underground trains -- near the Aldgate, Edgware Road and King's Cross stations -- went off at around 8:50 a.m. (0750 GMT), with the one on the bus exploding nearly an hour later.

At least 52 people died, although some reports have said the final toll could approach 70 as police continue to search the wreckage of one of the trains in a tunnel deep under London.

Fighting the problem at the source

In Prime Minister Tony Blair's weekly question time in parliament, he announced a plan to uproot the problem of religious extremism.

Ministers will begin consultations on planned counter-terrorism legislation within the next couple of weeks, Blair said.

Prior to the bombings -- the worst attack on British soil since World War II -- counter-terrorism proposals were denounced as a threat to civil liberties.

"We will look urgently at how we strengthen the procedures to exclude people from entering the UK who may incite hatred or act contrary to the public good, and at how we deport such people, if they come here, more easily," Blair said.

The prime minister also said his government would begin talks immediately with British Muslim leaders about combating the "poisonous and perverted misinterpretation of the religion of Islam" by mobilizing moderate opinion.