A suicide bomb blast in the centre of Istanbul has injured 32 people, including 15 policemen.
Police say the bomber tried to board a police bus in Taksim Square.
Seventeen civilians were also hurt.
Police identified other bombs nearby and have been working to disable them.
A large explosion was heard throughout central Istanbul just after 0900 GMT.
The explosion took place right next to the independence monument on Taksim Square, which is always crowded with people, our correspondent says.
There are usually squads of riot police posted at this part of the square, as it is often the site of demonstrations.
A police spokesman has said he believes they were the target of the explosion, which he said may have been caused by a suicide bomber.
Television pictures from Taksim Square showed body parts lying on the ground.
Eyewitness Aris Virkas told the BBC that he was walking through Taksim Square when he heard the blast.
"I turned around and saw policemen with blood on their face and someone lying on the ground," he said. "People, including police, were running around in panic.
"There was a big bus with maybe 20 police officers: they ran out of the bus, trying to find out what's going on.
"After a couple of minutes, they started asking people to step back."
Our correspondent says suspicion is likely to fall on Kurdish separatist factions, or groups linked to al-Qaeda.
"Those who threaten Turkey's peace, security and development will not be tolerated," said Prime Minister Recep Tayyip Erdogan on Sunday.
Mr Erdogan was in Mardin in south-eastern Turkey where most of the Kurdish minority live.
The Kurdish separatist PKK party has carried out bomb attacks in Istanbul in the past, as have extreme left-wing and Islamist groups.
The PKK went on ceasefire two months ago but that is due to run out on Sunday night.
However, PKK leaders have said recently that they will no longer target civilians.
Our correspondent says al-Qaeda-linked groups are small but active in Turkey, and police make frequent arrests. More than 100 suspected al-Qaeda militants have been arrested so far this year.
A group with ties to al-Qaeda carried out the bombing of the British consulate in Istanbul in 2003 in which 28 people died.
SOURCE: BBC http://www.bbc.co.uk/news/world-europe-11660795