An explosion in the heart of Istanbul's historic Sultanahmet tourist district killed at least ten people and wounded 15 on Tuesday and some local media reports said a suicide bomber may have been responsible.
Several bodies lay on the ground in the Sultanahmet square, close to the Blue Mosque and Hagia Sophia, a major tourist area of Turkey's most populous city. A police officer and witness at the scene reported also seeing several bodies and body parts.
Tourists from Germany and Norway were among the wounded, broadcaster CNN Turk said. An official from one tour company told Reuters a group from Germany was in the area at the time but said there was no immediate information on whether any of them had been injured.
The attack at the heart of one of the world's most visited cities comes as Turkey battles Kurdish militants in its southeast and Islamic State insurgents just across its southern borders in Syria and Iraq.
There was no immediate claim of responsibility but Kurdish, leftist and Islamist militants have all carried out attacks in Turkey in the past.
The Istanbul governor's office said the authorities were investigating the type of explosive used and who might have been responsible. It said ten people were killed and 15 wounded but gave no further details.
"We heard a loud sound and I looked at the sky to see if it was raining because I thought it was thunder but the sky was clear," said Kuwaiti tourist Farah Zamani, 24, who was shopping at one of the covered bazaars with her father and sister.
Turkey's AHaber television said the blast may have been caused by a suicide bomber but this was not independently confirmed. Ambulances rushed to the scene, ferrying away the wounded as police cordoned off streets, fearing a second attack.
"The explosion was very loud. We shook a lot. We ran out and saw body parts," one woman who works at a nearby antiques store said, declining to give her name.
"Terrorist links" suspected
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.
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 perpetrated 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 centres 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.