A bomb explosion on a busy pedestrian street on the outskirts of Istanbul wounded 31 people on Sunday, police said, in the latest violence to strike Turkey in recent weeks.
Istanbul's police chief Celalettin Cerrah said two civilians were in critical but not life-threatening condition and had been rushed to hospital for emergency surgery. He told reporters at the scene that two plain clothed policemen, patrolling the area, had been injured from broken glass.
There was no immediate claim of responsibility.
Istanbul - a popular tourism destination - has been struck by a series of bombings in recent weeks amid the worst street riots in more than a decade in Turkey's mainly Kurdish south east, which left 16 dead.
The bomb had been placed in a garbage bin in front of shops, cafes and kiosks in the busiest part of the pedestrian street in the Bakirkoy district on the European side of Turkey's largest city and near the international airport.
The blast blew out windows of stores in the street. The street was closed off and forensic experts were examining the area.
"Our friends are working. An assessment will be made according to the information received," Cerrah said.
Police fired into the air to disperse angry residents who initially thought a person taken in by the police was a bomber. Police said the person was a witness.
The Kurdistan Liberation Hawks (TAK), a shadowy group which has ties to the PKK, has claimed responsibility for a series of deadly bomb blasts in Istanbul. TAK, formed by former PKK guerrillas, has warned of further attacks.
Security has been stepped up across the country, which is seeking European Union membership. The armed forces have also moved a large number of troops to areas near the border with Iraq ahead of an expected offensive against PKK rebels.
More than 30,000 people, mostly Kurds, have been killed in the separatist conflict since the PKK took up arms against the state in 1984 with the aim of carving out an ethnic homeland.
The European Union and the United States, like Ankara, view the PKK as a terrorist group.