Explosion reported in central  Istanbul 

An explosion rocked a central square in Istanbul on Tuesday, Turkey's semi-official Anadolu news agency reported.

"Many police and ambulances sent to the scene" in Sultanahmet -- the heart of the city's heavily guarded tourist area, the news agency said.

Casualties were reported, but no further details were immediately available.

News reports showed Turkish security forces clearing the area.

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.