Police have confirmed that four detonations went off in London shortly before 1 p.m. local time. Scotland Yard has said that three London Underground stations have been closed, Warren Street, Oval and Shepard's Bush, after small explosions went off in trains in those stations. Service on a number of Underground lines has likewise been suspended although some have since reopened.

A bus which was traveling along Hackney Road in East London was also hit by an explosion. A spokesman from Stagecoach, which operates London's bus system, says the explosion was powerful enough to blow out the windows on the upper deck of the bus. Nobody was injured in that explosion and so far there have only been unconfirmed reports of one injury at Warren Street.

Prime Minister Tony Blair has called for calm. In a joint press conference, given with the Australian Prime Minister John Howard in London, shortly after the attacks, he said "we can't minimize instances like this which could have been very serious indeed. But these things are done to scare people and make them anxious and worried... It is important that we carry on with our normal lives and do what we want to do."

When asked by a journalist whether he felt that the attacks were a result of Britain's foreign policy in Iraq he replied that "the people responsible for the terrorist attacks are the terrorists."

Scotland Yard also confirmed that there was an event, to which armed police officers were responding, at University College Hospital near Warren Street station. A Reuters reporter said he saw three heavily armed policemen run into the main emergency entrance. That incident, however, has since come to an end.

Police are calling the explosions in London "clearly very serious incidents" and said there were "four attempts at explosion." A police spokesman also said the bombs seem to have been smaller than two weeks ago. Sir Ian Blair has said that the situation is under control and that no chemical weapons were involved.

So far there have been reports of only one injury, supposedly at Warren Street, but police say this is still unconfirmed.

The alert in London comes just two weeks after the violent terror attacks on July 7 which killed at least 56 people. Those attacks were allegedly the work of a terrorist cell in Britain itself and may have connections to the al-Qaida terror network.

This Thursday's explosions do not appear to have been on the scale of those attacks two weeks ago. There have been no eyewitness accounts of major damage to any of the trains that were hit although many report smelling smoke or the smell of burning rubber.

Reports from Warren Street indicate the explosion of a small nail bomb. An Italian man who spoke with Sky News said he witnessed the Warren Street Tube explosion just after the train arrived at the platform. The man told Sky News he had seen a man carrying a back pack which suddenly exploded. He described the detonation as minor. Some witnesses have said many subway passengers panicked as they were trying to rush out of the affected stations.