British Prime Minister Tony Blair is calling for calm following explosions at three London subway stations and a city bus earlier Thursday.

The British leader called the explosions an attempt to frighten Londoners and urged citizens to return to business as normal.

London's police commissioner Ian Blair called the incidents very serious but said there were very few injuries and the bombs were much smaller than the explosions which occurred two weeks ago in London. He urged Londoners to remain where they are while authorities investigate.

Service has been suspended on at least three subway lines.

Armed police also entered a hospital near one of the incidents cordoning off the building.

The noontime explosions come exactly two weeks after a series of blasts on subway trains and a city bus killed at least 56 people.

Some information for this report provided by AP.