A suicide bomber has killed at least 10 people, most of them German tourists, in Istanbul's historic heart, in an attack Prime Minister Ahmet Davutoglu has blamed on Islamic State.
All of those killed on Tuesday in Sultanahmet square, near the Blue Mosque and Hagia Sophia - major tourist sites in the centre of one of the world's most visited cities - were foreigners, Davutoglu said.
A senior official said nine were German.
Deputy Prime Minister Numan Kurtulmus said the bomber was believed to have recently entered Turkey from Syria but was not on Turkey's watch list of suspected militants.
He said earlier that the bomber had been identified from body parts at the scene and was thought to be a Syrian born in 1988.
Davutoglu said he had spoken by phone with German Chancellor Angela Merkel to offer condolences and vowed Turkey's fight against Islamic State, at home and as part of the US-led coalition, would continue.
"Until we wipe out Daesh, Turkey will continue its fight at home and with coalition forces," he said in comments broadcast live on television, using an Arabic name for Islamic State.
He vowed to hunt down and punish those linked to the bomber.
Several bodies lay on the ground in the square, also known as the Hippodrome of Constantinople, in the immediate aftermath of the blast.
People believed to be German tourists that were targeted at an explosion in the historic Sultanahmet district are escorted back to their hotel in Istanbul, Tuesday, Jan. 12, 2016. Source: AAP
It was not densely packed at the time of the explosion, according to a police officer working there, but small groups of tourists had been wandering around.
"This incident has once again shown that as a nation we should act as one heart, one body in the fight against terror. Turkey's determined and principled stance in the fight against terrorism will continue to the end," President Tayyip Erdogan told a lunch for Turkish ambassadors in Ankara.
Norway's foreign ministry said one Norwegian man was injured and was being treated in hospital. The Dogan news agency said nine Germans and one Peruvian were also wounded.
Turkey, a NATO member and candidate for accession to the European Union, is part of the US-led coalition against Islamic State fighters who have seized territory in neighbouring Syria and Iraq, some of it directly abutting Turkey.
There was no immediate claim of responsibility but Islamist, leftist and Kurdish militants, who are battling Ankara in southeast Turkey, have all carried out attacks in the past.
"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.
The dull thud of the blast was heard in districts of Istanbul several kilometres away, residents said.
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.
