Ramadan is off to a flying start as an explosion in the tourist district kills eleven and injures eight.
Turkish officials say a police bus was targeted in the central Istanbul district of Vezneciler with some wounded in the blast.
A number of gunshots were reportedly heard after the explosion and police have evacuated shops, cafes and homes near the scene
A parked car packed with explosives was detonated by remote control as the police bus passed by.
The area is a major draw for tourists from around the world who flock to the historic city to marvel at the sights.
The explosives were remotely detonated as the vehicle passed through the busy Vezneciler district at the morning rush hour, reports said.
No group has said it carried out the attack.
Violence in Turkey has escalated recently as a result of tensions with Kurdish separatists and the conflict in neighbouring Syria.