Metropolitan police have released CCTV images of four men they are urgently trying to trace in connection with yesterday's failed bomb attacks in London.
They urged anyone who may know the men not to approach them but to contact police immediately.
One image shows a man running from Oval tube station. The distinctive 'New York' top he is seen wearing was later found discarded in Brixton.
The other images show another suspect on the top deck of the bus on which a rucksack bomb was left and two men leaving two other stations after their rucksack bombs failed to explode.
Meanwhile, police investigating yesterday's attacks have arrested a man in Stockwell in the south of the city.
The arrest comes after police shot dead a man in Stockwell Underground Station earlier today.
Eyewitnesses said an Asian man was pursued by three armed plainclothes officers into Stockwell tube station. He leapt over a barrier and was chased onto a train.
According to one eyewitness on the train two plainclothes officers pushed the man to the floor while a third officer shot the man five times with a semi-automatic pistol.
Stockwell Tube Station was evacuated and Victoria and Northern Lines services, which pass through it, were suspended.
House search in attempted attacks probe
In another development, Scotland Yard has confirmed that detectives investigating yesterday's attempted bombings searched an address in the Harrow Road area of West Kilburn.
Armed police were reported to have told residents around Harrow Road to stay off the streets. One witness told the BBC News that he saw remote controlled trucks that he thought were used by bomb disposal units.
Earlier, armed police surrounded a mosque in east London following a telephone threat saying a bomb had been left there.
Forensic experts examine explosives
Three of the four devices found yesterday are thought to be of similar size and weight to the bombs used in the 7 July attacks in which 56 people were killed.
The fourth was smaller and appears to have been contained in a small plastic box.
In the case of three of the devices, it appears the detonators went off but that the bombs failed to explode.
Forensic experts are now trying to establish if the explosive is linked to that found in a house in Leeds following the blasts in London two weeks ago.
As on 7 July, the attacks were almost simultaneous and were carried out at three underground stations and on a bus.
Concern has again being expressed about the quality of intelligence on terrorist activities in Britain.
However a former Chairman of the UK's Joint Intelligence Committee, Dame Pauline Neville-Jones, said tracking down terrorists was something that took time.
