Police were trying to work out Wednesday whether four young British Muslims suspected of carrying out suicide attacks in London last week were inspired by a master bomber who may still be at large.

Anti-terrorist police have said it would be "remarkably reckless" to rule out further attacks in Britain - despite Tuesday's stunning breakthrough in the bid to track down those who carried out the killings.

"We have to assume there are others who are ready to do the kinds of things that these people did last Thursday," Home Secretary Charles Clarke told BBC radio.

The police investigation is expected to focus on the towns and cities of West Yorkshire, in northern England, where three of the four bombers are known to have lived.

The region has a big Muslim population, and police will try to establish whether it is harbouring a cell or an operative, possibly from al-Qaida, who might have planned the bombings which killed at least 52 people and injured 700.

Media reports suggest the four bombers were aged between 19 and 30 and were so-called "cleanskins" - with no convictions or known terror involvement. The suspects were all believed to be British nationals, of ethnic Pakistani origin.

Police say it is "very likely" that one of the four died in the blasts on London's transport network, and it is possible that all four blew themselves up deliberately.

If they did, it would be the first time that suicide bombers, who have wreaked carnage from the streets of the United States to Iraq, have struck in Western Europe.

Shocked friends and neighbours said they were ordinary youths, more interested in sport than politics.

"He was a sweet guy who gets on with everyone," was one description of one of the suspects, a 22-year-old sports science graduate who occasionally helped out in his father's fast food shop in the city of Leeds.

The Muslim Council of Britain said it was stunned that English Muslims appeared to have carried out the attacks. "We have received today's terrible news from the police with anguish, shock and horror," Secretary-General Iqbal Sacranie said in a statement.

"Nothing in Islam can ever justify the evil actions of the bombers."

The four travelled to London on the day of the blasts and were seen on closed-circuit television carrying rucksacks at King's Cross rail station shortly before 8:30 am, police said.

A police source said they looked relaxed, more like they were going on a hiking holiday than a suicide mission.

Police seized explosives after searching houses in the Leeds area and arrested a relative of one of the suspects. The relative was brought to London for questioning.

They also towed away a car in Luton, just north of London, which they said was linked to the bombings.

The government says last Thursday's attacks on three trains and a bus bear the hallmark of Osama bin Laden's al-Qaida network, blamed for the 9/11 attacks on the United States and the Madrid bombings last year.

Alex Standish, editor of Jane's Intelligence Digest, said that if the suicide bombing theory was confirmed, Britain - accustomed in recent decades to bombings by the nationalist Irish Republican Army - would have crossed a new threshold.

Source: China Daily