A bomb explosion rocked a bus carrying military personnel over a bridge in Istanbul on Thursday, but nobody was hurt in the blast, NTV television said.
Turkish television later showed pictures of the bus, which appeared largely intact, suggesting the bomb may have been only a small explosive device.
The blast occurred in the district of Kucukcekmece on the western outskirts of Turkey's largest city, which suffered a series of devastating bomb explosions last November pinned on Islamist militants linked to the al-Qaida network.
The bus and two other vehicles were damaged in Thursday's blast, which occurred at 7.30 am (0430 GMT), and terrorism experts were at the scene, NTV said.
Police were searching for one suspect in the area. It was not immediately clear whether the bomb had been concealed on the bus or had been placed on the road.
A diverse array of small far left-wing, militant Islamist and pro-Kurdish groups operate in Turkey and have carried out mostly small-scale attacks, often on military or other official targets.
But last November's blasts, striking British and Jewish targets in Istanbul, were on a completely different scale for this Muslim but secular country which has close security ties with the United States and Israel.
More than 60 people were killed in those blasts, for which Osama bin Laden's al-Qaida organization claimed responsibility.
Security remains a major issue for Istanbul as it prepares to host a NATO summit in June which will be attended by U.S. President George W. Bush and other top Western leaders.
