ISTANBUL, June 24: Bombs exploded in Turkey's two main cities on Thursday - two days before a visit by US President George Bush to Ankara and a Nato summit in Istanbul, killing four people and injuring at least 18 others.

The White House said there would be no change to Bush's schedule despite the blasts. Istanbul Governor Muammer Guler told reporters the bomber in Istanbul was a woman carrying the device in her lap when it exploded on board a bus outside a hospital in the Fatih district.

"The bus was not the target. The bomb was being carried from one place to another... We suspect a Marxist-Leninist group." The blast killed four people, including the bomber, and injured 15, said a surgeon.

Police detained three suspects in connection with the explosion. A small explosive device went off earlier outside the Hilton Hotel in Ankara, where Mr Bush is due to stay on Saturday before he leaves for Istanbul. -Reuters