Police shot a man dead at a London underground rail station today during a hunt for four men who attempted to bomb trains and buses in the city yesterday.
Police also asked for help in tracing four men in connection with the attacks that caused chaos but killed no one in yesterday's apparent bid to repeat the July 7th attacks that killed 52 rush-hour commuters.
One man was arrested in connection with yesterday's explosions this evening near Stockwell underground station, where the man was shot earlier, police said. They declined to comment on whether the man detained was one of the four the were seeking.
Combination picture taken from CCTV and released by London's Metropolitan Police of the four suspects sought in connection with yesterday's attempted bomb attacks
Police issued photos of the four suspects taken by closed-circuit television cameras on London's transport network.
It was not clear whether the man shot dead today in south London was suspected of involvement in the failed bomb attacks or had been mistaken for someone else. This afternoon, Metropolitan Police chief Ian Blair told a news conference the man shot was "directly linked to the ongoing and expanding anti-terrorist operation".
However, this evening, police said it was still unclear whether the man they shot dead earlier in the day was one of the four wanted men. "The man shot at Stockwell station is still subject to formal identification and it is not yet clear whether he is one of the four people we are seeking to identify and whose pictures have been released today," police said in a statement.
The police said all deaths related to police operations were a matter of deep regret. "Nevertheless the man who was shot was under police observation because he had emerged from a house that was itself under observation because it was linked to the investigation of yesterday's incidents," the statement said.
"He was then followed by surveillance officers to the station. His clothing and his behaviour at the station added to their suspicions." An investigation into the circumstances of his death was under way, it said.
Witnesses spoke of panic as a man of south Asian appearance wearing a heavy jacket vaulted over barriers at Stockwell station as he was chased, tackled, then shot.
Commuter Teri Godly said she stood next to the man early on Friday before police charged in. "A tall Asian guy, shaved head, slight beard, with a rucksack got in front of me. Shortly after that, as I was about to get onto the train, eight or nine undercover police with walkie talkies and handguns started screaming at everyone to 'get out, get out'," she told Sky News television.
"I've never seen anything like it in my life. I saw them kill a man basically. I saw them shoot a man five times," witness Mark Whitby told BBC television.
"The other passengers were distraught. It was just mayhem, people were just getting off the Tube ... People running in all directions, looks of horror on their faces, screaming, a lot of screaming from women, absolute mayhem."
Witnesses said there was confusion as shocked passengers tried to work out what was happening. One man spoke of a strange smell that seemed to be coming from a smoking bag on the train.
The Abu Hafs al Masri Brigade, an al Qaeda-linked group that claimed responsibility for the July 7th bombings, said in a statement on an Islamist Web site it was behind the attacks.
"Our attack in the heart of the infidel British capital is nothing but a message to all European governments that we will not rest until all the infidel troops leave Iraq," said the group, whose claims of responsibility for previous attacks in Europe have been discredited by security experts.
As forensics experts studied the three underground trains and a double-decker bus hit by the small, near-simultaneous explosions, police were called to a series of security alerts.
In Harrow Road in west London, armed police searched a house. A police spokeswoman said no arrests had been made. Police said they were conducting two other raids.
In New York, commuters faced random searches of backpacks and packages as police stepped up checks.
British police have more clues from yesterday's attacks, including the unexploded bombs, witness reports and CCTV footage, than they had after the July 7th suicide bombs that killed 52 commuters and the four bombers and wounded 700.
Research published by tourist group VisitBritain said Britain could lose at least £300 million pounds (€430 million) in lost tourism revenues due to the attacks.