Sir Ian told Sky News: "This is a tragedy. The Metropolitan Police accepts full responsibility for this. To the family I can only express my deep regrets."

He said there was no reason to believe the four men sought over the failed bombings - whose images caught on CCTV were released on Friday - had left the country.

He acknowledged "somebody else could be shot" as the hunt continued, but added "everything is done to make it right".

But he said the "shoot to kill" policy for dealing with suspected suicide bombers would remain in force.

'Difficult circumstances'

Mr Clarke told the BBC: "I very, very much regret what happened.

"I hope [the family] understand the police were trying to do their very best under very difficult circumstances."

On the ongoing police investigation into the bombings, he said "good progress" was being made thanks to the "tremendous support" from the public.

Mr Clarke also said he was postponing joining his family on holiday because of the current crisis.

Foreign Secretary Jack Straw said: "It is obviously deeply regrettable but what we have to appreciate is the very intense pressure under which the police officers have to work".

But Mr Menezes's family is struggling to come to terms with his death.

'Police incompetence'

Mr 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".

He said Mr Menezes was from the city of Gonzaga in Minas Gerais state and had lived in London for over three years.

Mr Menezes' grandmother, Zilda Ambrosia de Figueiredo, told Globo TV "there was no reason to think he was a terrorist".

The body of Mr Menezes will be taken back to Brazil as soon as possible, according to relatives.

Brazil's foreign minister Celso Amorim met officials at the Foreign Office in London on Sunday to seek an explanation for the shooting.

'Shocked and perplexed'

"The Brazilian government and the public are shocked and perplexed that a peaceful and innocent person should have been killed," he said.

"Brazil is totally in solidarity with Britain in the fight against terror but people should be cautious to avoid the loss of innocent life."

He spoke by phone to Mr Straw, who he said promised a full investigation into the death.

"I said that was very important. We can't recover the life of the Brazilian citizen who has been killed, but we can discover the details."

Mr Amorim is due to meet Mr Straw in person on Monday evening.

The BBC's correspondent in Brazil, Tom Gibb, said Mr Menezes had lived for a time in a slum district of Sao Paulo and that could explain why he had run from the police.