London (CNSNews.com) - Rush-hour traffic has been severely disrupted in central London Thursday as police sweep the Vauxhall area for clues after Wednesday night's explosion at the headquarters of the foreign intelligence service, MI6.
Alan Fry, head of the police anti-terrorism squad, said early Thursday a small missile had been fired at the building, a landmark alongside the River Thames, hitting the eighth floor.
The building suffered minimal damage. It was designed to withstand bombs.
No group has claimed responsibility for the attack, and Fry said he could not say who was behind it.
"Clearly I have to keep in mind the capability of dissident Irish groups, but at this stage I would not be ruling out any other group who might see the secret intelligence service as a potential target.
"The sheer nature of work of the secret intelligence service must mean that there are other terrorist groups throughout the world who might see their premises as a potential target," he added.
The entire area surrounding the building has been sealed off while investigations continue. Train services from nearby Waterloo station, including the international Eurostar service to Paris via the Channel Tunnel, have been cancelled.
Fry warned that there was a "genuine threat of terrorism in London."
Two small bombs in the capital during the summer raised fears of a new mainland bombing campaign by dissident Irish republican groups opposed to the Good Friday peace process.
One bomb exploded under a bridge in Hammersmith in June, another was found on an underground (subway) station a month later. A group calling itself the "Real IRA" was believed responsible for both.
The MI6 building, one of the most securely-guarded, featured in the James Bond move "The World is Not Enough," when it was blown up in a sequence involving a 80 mile-an-hour speed boat chase down the Thames.
Architecture critics have nicknamed the futuristic building "Babylon-on-Thames."