A number of London underground stations have been evacuated and lines closed after minor blasts happened at three tube stations and a bus on Thursday

Metropolitan Police Commissioner Ian Blair said the four bombs appeared to be small and that the situation was coming under control. He said only three tube lines were still suspended and it was time London started to return to normal.

Prime Minister Tony Blair said the attacks were designed to make people anxious.

"We know why these things are done. They are done to scare people," Blair said in a joint news conference.

"Fortunately in this instance there appear to have been no casualties ... We've got to react calmly," he added.

Earlier, passengers reported one blast at Warren Street station, central London. The Scotland Yard said one was injured in the explosion using a nail bomb.

Police cordoned off large areas around Warren Street, Oval and Shepherd's Bush Tube stations, in the city center after reports of smoke coming from two of the stations.

The whole of the Northern Line has been suspended, along with the Victoria Line and the Hammersmith and City line.

In addition, a blast was reported on the top deck of a Number 26 bus in Hackney Road in east London. There were no injuries and the bus suffered no structural damage.

Eyewitnesses heard bangs and saw abandoned rucksacks at the sites of the three tube stations as well as the number 26 bus.

Police said armed officers had been deployed to University College Hospital, close to Warren Street Station, after an incident.

The hospital has not received any casualties or been alerted to casualties.

There were reports that a memo had been circulated to staff to look out for a black or Asian man with wires sticking out of his top.

Meanwhile, a man was arrested near Blair's Downing Street office by armed police and led away.

Due to the explosions, a number of other stations are still closed including Great Portland Street, Westminster, Waterloo, St Paul's and Oxford Circus tube stations, as well as Waterloo tube station and King's Cross.

The blasts on Thursday came exactly two weeks after more than 56 people were killed and over 700 people injured in blasts on underground railway trains and a bus in London.

Source: Xinhua