Turkish media said an explosion Tuesday hit a historic district in central Istanbul, causing casualties.
The cause of the blast and the extent of the casualties in the Sultanahmet area were not immediately clear.
Turkey has been on alert for attacks since an October double suicide bombing killed more than 100 people at a gathering of peace activists outside a train station in the capital, Ankara.
The government cancelled planned New Year’s celebrations in Ankara after detaining two suspected Islamic State members believed to be planning suicide attacks.
Turkish forces have also been carrying out an offensive against the outlawed Kurdistan Workers Party, which has been blamed for attacks including those targeting police and soldiers.