The head of Britain's anti-terrorist branch, Peter Clarke, said the two were Yasin Hassan Omar and Muktar Said-Ibrahim or Muktar Mohammed-Said. He gave details of where the two others fled after their bombs failed to explode last Thursday.

"I hope that by setting out some of what we have been able to learn over the past few days, the public may be able to
contribute even more to the progress of the investigation," Clarke told a news conference.

Arrests

Police said they had arrested two people on Monday, taking the total number of those in detention to five, and armed officers raided an apartment in north London that had been visited by one of the suspects. But they made no arrests.

Police warned that the bombers
could strike again

The police said the arrests and the search were in connection with the failed bombings of three Underground trains and a bus last Thursday, exactly two weeks after bombers killed 52 people in an attack officials linked to al-Qaida.

But they were still searching for the four prime suspects.

"We are still looking for four men," a spokesman said.

Manhunt continues

London police were keen to shift the focus back to what they called the biggest manhunt in their history after mistakenly shooting dead a Brazilian electrician they believed to be a suspected bomber.

The anti-terrorist branch gave
names of two of the suspects

A police spokeswoman said the bombers "may strike again so it is a race against time. It is still a very fluid situation. The inquiry is moving at a rapid pace".

"There is no reason to believe they have left the country. They could be harboured in safe houses." 
 
Weekend newspapers were full of the grainy closed-circuit television pictures of the four suspects and police asked the public for help in tracing the men.

Shoot to kill

But the investigation was dealt a blow and the reputation of British police severely tarnished when the Brazilian was shot dead by mistake on Friday.

Prime Minister Tony Blair said: "We are all desperately sorry for the death of an innocent person. I understand entirely the feelings of the young man's family."

The police apologised for the
shooting of the Brazilian man

"If this had turned out to be a terrorist and they (the police) had failed to take that action, they would have been criticised the other way," Blair told reporters.

Jean Charles de Menezes, 27, was shot five times in the head after being chased onto an Underground train by undercover police, witnesses said.

Police said Menezes had been followed from a block of apartments in south London that had been under surveillance since the 21 July  attacks and was shot after running away from armed police who had ordered him to stop.

Innocent person killed

Brazilian Foreign Minister Celso Amorim, who will meet his British counterpart Jack Straw later on Monday, said: "The Brazilian government and the public are shocked and perplexed that a peaceful and innocent person should have been killed."

Despite the concerns of human rights activists, police say they will not abandon what they called their "shoot-to-kill in order to protect" policy with suicide bombers. They have warned that more people could be killed during the investigation.

An opinion poll in the Daily Mirror suggested Britons believe their country's support for the Iraq war contributed to the London bombings, something Blair has denied.

Nearly a quarter of those polled said Iraq was the main cause for the bombings, with 62 % saying it was a contributory factor.