Five people have been injured by a blast which targeted a police bus in central Istanbul, Turkish media say.
The remote-controlled device was reportedly detonated as the vehicle passed through the Vezneciler district.
Pictures showed the wreckage of a bus destroyed and the facade of nearby buildings damaged.
Violence in Turkey has escalated recently as a result of tensions with Kurdish separatists and the conflict in neighbouring Syria.
The explosion happened during the morning rush hour, near the city’s historic Bayezit Square neighbourhood, a major tourist attraction.
Television images showed armed police in the street near to the site.
No group has said it carried out the attack.
Recent attacks in Turkey
- March 2016: 35 people killed by Kurdish militants in Ankara; 4 dead in a suicide attack in Istanbul
- February 2016: 28 killed in military convoy in Ankara
- January 2016: 12 German tourists are killed in a suspected IS suicide bombing in Istanbul
- October 2015: More than 100 people are killed in a double suicide bombing at a Kurdish peace rally in Ankara
Both the so-called Islamic State (IS) and Kurdish militants have said they were behind recent attacks in Turkey.
President Recep Tayyip Erdogan has said terror groups are targeting civilians because they are losing their struggle against Turkish security forces.
Turkey is part of the US-led coalition against IS and allows coalition planes to use its air base at Incirlik for raids on Iraq and Syria.
And a two-year-old ceasefire between Turkey and the Kurdish militant PKK broke down last summer.