British police remain under orders to shoot suspected suicide bombers in the head if necessary, London's police chief Ian Blair said Sunday, despite having mistakenly killed an innocent man.

When asked by Sky Television if the police had shoot-to-kill instructions in such cases, Blair replied: "They have to be that. Because there's no point in shooting at somebody's chest because that's where the bomb is likely to be."

He added: "There's no point in shooting anywhere else because if they fall down they detonate it. It is drawn on the experience from other countries including Sri Lanka."

"The only way to deal with this is to shoot to the head," the Metropolitan Police commissioner said.

Blair expressed "deep regrets" over Friday's incident when police mistakenly shot a Brazilian man during a chase onto a subway train in south London, a day after a new wave of attempted bombings.

Brazil's foreign ministry demanded an explanation into the "lamentable error" which saw 27-year-old electrician Jean Charles de Menezes pursued through a subway station before being cornered and shot repeatedly in the head.

The country was "outraged and amazed" that the man was mistakenly shot by police, a statement issued by the Brazilian foreign ministry said.

Menezes' family is said to be shocked by the circumstances surrounding his death.

His cousin, Alex Alves Pereira, from London, told the BBC: "Apologies are not enough. I believe my cousin's death was result of police incompetence." Describing his cousin as a "person full of life" he said his cousin was "a victim of government's mistakes."

Britain's Muslims wary

British Islamic groups called for a public inquiry into the shooting, worried that the Asian ethnic origin of some of the bombers could see Muslims targeted by police.

Dr Azzam Tamimi, from the Muslim Association of Britain, told BBC News the police should review their procedures. "It is human lives that are being targeted whether by terrorists or whether in this case unfortunately by people who are supposed to be chasing or catching the terrorists," Tamimi said. "This is very frightening, people will be afraid to walk the streets now."

Massoud Shadjareh, head of the London-based Islamic Human Rights Commission, called for a full public inquiry. "How can you shoot someone on mere suspicion? You can't even put someone in prison on suspicion, how can you kill them like that?" he said.

"A cornered rabbit"

But newspapers and London's mayor called for understanding. The carnage of the July 7 bombings, in which four suicide attackers and 52 others died, and the near-miss Thursday when bombs used in a repeat attack seemingly failed to explode properly, meant police faced an impossible situation, they said.

"The police acted to do what they believed necessary to protect the lives of the public. This tragedy has added another victim to the toll of deaths for which the terrorists bear responsibility," London mayor Ken Livingstone said.

Terrified subway passengers scattered in panic on Friday morning as plain-clothed police pursued Menezes, who relatives said was going to work, through Stockwell Underground station in south London.

Witnesses said the Brazilian -- described as looking "like a cornered rabbit" -- fell to the floor in a train carriage before a policeman standing directly above shot him five times in the head.

Police faced tough choice

"For somebody to lose their life in such circumstances is a tragedy and one that the Metropolitan Police Service regrets," London's police force said Saturday in their first admission they had killed an innocent man.

Initially, police said Menezes was linked to Thursday's attacks, noting that he was wearing a thick coat on a warm summer day, prompting fears he could be carrying explosives.

Sunday's newspapers agreed that however tragic the outcome, it was difficult to blame police for taking the action they did.

If a suicide bomber is merely wounded "he can massacre in his final seconds of consciousness", The Mail on Sunday noted in its editorial. "In the London of July 2005, few would want the police to take any chances. And bear in mind that if the Stockwell suspect had been wearing a suicide belt, the officers who shot him would be lauded as heroes and loaded with medals, as well as the thanks of a grateful public."

Probe gathers speed

As the controversy raged, the police investigation into the bombings appeared to be advancing at speed, with much information gathered from the four failed rucksack-based bombs abandoned on Thursday.

According to The Observer newspaper, documents found in one of the rucksacks have led police towards a potentially vital clue -- a possible link between the two sets of attackers.

According to the paper, some of the suspected bombers from Thursday are believed to have been on a whitewater rafting trip in Wales attended by two of the July 7 bombers, Mohammad Sidique Khan and Shahzad Tanweer. The trip could even have been a "bonding" exercise for all concened, meaning the attacks were planned jointly, the paper said.

Two men have now been arrested in what has become one of Britain's biggest-ever manhunts. Both were detained during raids Friday in Stockwell, near where the Brazilian man was shot.

Police said Saturday that almost 500 people had called them after they released security camera images of the four suspected bombers, which were plastered over the front pages of Saturday's press.

"Detectives are now working through the information from the phone calls and e-mails and are hopeful that there will be significant lines of enquiry to follow," a police statement said.

Additionally, officers raided an apartment in the Streatham area of south London, not far from Stockwell.

London remains on edge

But nerves remained on edge in the British capital.

A park in northwest London was cordoned off Saturday as police said they were investigating a suspect package found there, which according to one report had nails and bolts packed around it and wires protruding.

An examination "suggests that the object may be linked to devices found" on Thursday, police said in a statement.

Adding to the concerns, two Britons were feared dead after suicide car bombers struck Egypt's Red Sea tourist resort of Sharm el-Sheikh, killing at least 88 people.