An explosion rocked a central square in Istanbul on Tuesday, killing at least 10 people and wounding 15 others, the Istanbul governor's office said. "Many police and ambulances sent to the scene" in Sultanahmet Square -- the heart of the city's heavily guarded tourist area, Turkey's semi-official Anadolu news agency said.
News reports showed Turkish security forces clearing the area. No group immediately claimed responsibility.
The blast comes at a time Turkey is dealing with multiple threats to its security. ISIS and the Kurdish-group the PKK have been mentioned in recent outbreaks of violence.
In October, two explosions hit a lunchtime peace rally in Ankara, which called for an end to the renewed conflict between the Kurdistan Workers' Party, or PKK, and Turkish government. Ninety-nine people were killed more than 240 were injured. ISIS is active in neighboring Iraq.
The Turkish government allows the United States to launch strikes on ISIS positions from Incirlik Air Base in southern Turkey. Kurdish forces have been battling ISIS across a swath of northern Iraq and Syria.