Turkish Police detained four people in a hunt for the perpetrators of a car bombing in central Istanbul on Tuesday that killed seven police and four civilians, State media said.
The third deadly attack in Turkey's biggest city in six months targeted a bus transporting anti-riot police in Beyazit district, close to many of the city's top tourist sites, Istanbul governor Vasip Sahin said on Turkish television.
Thirty-six people were wounded, three of them seriously, he added.
The four suspects were taken to police headquarters in Istanbul for interrogation, state-run Anatolia agency said, without providing further information.
There was no early claim of responsibility, but President Recep Tayyip Erdogan suggested the outlawed Kurdistan Workers' Party (PKK) was behind the attack.
For the PKK to target major cities such as Istanbul "is nothing new," he said after visiting the injured at an Istanbul hospital.