TERRORIST SUSPECTED

The torrorist suspect

Prime Minister Ahmet Davutoglu held an emergency meeting in Ankara with the interior minister and security chiefs. A senior official said "terrorist links" were suspected in the attack, but declined to comment further.

The dull thud of the explosion was heard in districts of Istanbul several kilometers away, residents said. Tourist sites including the Hagia Sophia and the nearby Basilica Cistern were closed on the governor's orders, officials said.

The sound of the call to prayer rang out from the Blue Mosque as forensic police officers worked at the scene.

Just over a year ago, a female suicide bomber blew herself up at a police station for tourists off the same square, killing one officer and wounding another. That attack was initially claimed by a far-left group, but officials later said it had been carried out by a woman with suspected Islamist militant links.

Turkey has become a target for Islamic State, with two bombings last year blamed on the radical Sunni Muslim group, in the town of Suruc near the Syrian border and in the capital Ankara, the latter killing more than 100 people.

Violence has also escalated in the mainly Kurdish southeast since a two-year ceasefire collapsed in July between the state and the Kurdistan Workers Party (PKK) militant group, which has been fighting for three decades for Kurdish autonomy.

The PKK has however generally avoided attacking civilian targets in urban centers outside the southeast in recent years.

"Ambulances started rushing in and I knew it was a bomb right away because the same thing happened here last year," said Ali Ibrahim Peltek, 40, who operates a kiosk selling snacks and drinks on the square.

"This is not good for Turkey but everyone was expecting a terrorist attack," he said.

Davutoglu's office imposed a broadcasting ban on the blast, invoking a law which allows for such steps when there is the potential for serious harm to national security or public order.ı