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

In interviews on Wednesday, Home Secretary Charles Clarke, who is visiting Brussels to confer with his European Union counterparts, said the four were suicide bombers and the police were now hunting for those who worked with them.

In an interview with BBC Radio, Clarke said: "We have to attack the people who are driving, organising and manipulating those people.

"And that's, of course, where the police investigation is going just at this moment."

Al-Qaida connection?

The home secretary said the nature of the organisation behind the attacks was hazy, without ruling out previous government suspicions that they were linked to or inspired by Osama bin Laden's al-Qaida organisation.

Citing experts, he said: "Al-Qaida is changing into a range of different types of organisation with different foci, different approaches in different parts of the world.  

Foreign Secretary Jack Straw
talks to EU on improving security

"It is understanding that more anarchic network that we have to achieve," he said, adding he did not know what the nature of the relationship of the four men was to people more widely.

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

He said the authorities must tackle the roots of the problem by dealing with "anybody who preaches the kind of fundamentalism ... which can lead four young men to blow themselves and others up on the Tube on a Thursday morning".

Newspapers name bombers

A series of newspapers named two of the dead suspected bombers as Hasib Hussein, 19, and 22-year-old Shehzad Tanweer, who lived in Leeds.

The Daily Mail said Hussein carried the bomb that exploded on a packed double-decker bus in central London, while Tanweer detonated a device on the London Underground near Edgware Road station, to the west of the city centre.

The paper named 30-year-old father of one Mohammed Sadique Khan, also from Leeds, as having been responsible for another underground blast near Aldgate station, just east of the city centre.

The Independent newspaper, however, identified the Edgware Road attacker as Eliaz Fiaz, 30, from Dewsbury, a town near Leeds.

All the reports, which cited a variety of intelligence and police sources, said the bombers travelled to London's central King's Cross station together by commuter train from Luton, a town just north of the capital.

Above suspicion

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.

The bombs on the London Underground trains - near Aldgate, Edgware Road and King's Cross stations - went off at around 8.50am, 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 remains of one of the trains in a tunnel deep under London.