"We are now satisfied that he was not connected with the incidents of Thursday 21st July 2005," police said in a statement.

"For somebody to lose their life in such circumstances is a tragedy and one that the Metropolitan Police Service regrets," the police said.

Police hunting four men who tried to bomb London's transport system on Thursday -- two weeks after suicide bombers killed 52 commuters -- shot dead the man who had been under surveillance and refused orders to halt.

The killing at point-blank range with five shots to the head in front of shocked passengers on a packed underground train triggered speculation that traditionally unarmed police had radically changed their iron-fist-in-velvet-glove approach.

"The man emerged from a block of flats in the Stockwell area that were under police surveillance as part of the investigation into the incidents on Thursday 21st July.

"He was then followed by surveillance officers to the underground station. His clothing and behaviour added to their suspicions," the statement said.

It added that the circumstances that led to the man's death were being investigated.

The killing had already been condemned by Muslim groups, who expressed shock at the news of the victim's innocence.

"To give license to people to shoot to kill just like that, on the basis of suspicion, is very frightening," Azzam Tamimi of the Muslim Association of Britain told BBC television.

"It is human lives that are being targeted here, whether by terrorists or in this case unfortunately by people who are supposed to be chasing or catching the terrorists."

Former Scotland Yard (London police) commander John O'Connor told the BBC: "It is a shocking incident, and I think the consequences may be graver if he turns out to be a young Muslim."