The London [Images] police on Friday said that the shooting at a tube station in south London in which a suspected militant was killed was 'directly linked' to Thursday's attacks on the transport system in London.

The man was challenged by armed officers and gunned down at the Stockwell tube station after he refused to obey instructions, Metropolitan Police Commissioner Ian Blair told a press conference.

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He said the shooting was part of the operation against those responsible for Thursday's minor explosions on three
tube trains and a double-decker bus.

The police also released closed circuit images of four men they were 'urgently seeking' in connection with Thursday's attacks.

• Police shoot man at London subway station

Making it clear that Friday's operation was targetted against criminals, Blair said it was not against any community and appealed for calm.

"The situation is under control," he said.