A suicide bomber wounded 32 people in an attack targeting Turkish police in Istanbul's main square on Sunday, an area teaming with tourists and shoppers.
No organisation has claimed responsibility, officials said, though the city has been targeted in the past by Kurdish separatist militants and al Qaeda, as well as militants from Turkey's far-left.
Istanbul police chief Huseyin Capkin said a man had approached police stationed at the square before blowing himself up. Television footage immediately after the explosion appeared to show police firing warning shots and people fleeing in panic.
Fifteen policemen and 17 civilians were wounded in the attack at 10.40 a.m. in Taksim Square, but only nine, mostly police, were kept in hospital, Istanbul Governor Huseyin Avni Mutlu told reporters.
Taksim Square is a tourist and transport hub surrounded by restaurants, shops and hotels, at the heart of modern Istanbul.
The bomber struck near police buses parked close to a monument commemorating Mustafa Kemal Ataturk, the founder of modern Turkey, and victory in the war of independence in 1923.
The police presence in Taksim is raised around national holidays like Republic Day, which was celebrated on Friday.
Cellphone footage taken just after the explosion showed a woman lying close to the monument bleeding heavily from her leg, and a policeman lying with blood streaming from his head.
A taxi driver told CNN Turk news channel he saw a 30 to 33-year-old man approach the police to ask directions, at which point the bomb detonated. Another witness said he saw two men.
According to the governor, police seized plastic explosives found with a detonator at the scene, though it was unclear whether they had been part of a second bomb.