At least 10 people have been killed in an explosion at central Istanbul's historic Sultanahmet Square, the city governor's office said.
The explosion occurred at about 10.20am local time on Tuesday morning, hitting an area popular with both tourists and locals. In a statement, the Istanbul governor's office said 10 people were killed and 15 were injured.
"Investigations into the cause of the explosion, the type of explosion and perpetrator or perpetrators are under way," it said in a statement quoted by the Dogan news agency.
Turkey explosion: Deadly blast strikes Istanbul tourist district
Turkish President Recep Tayyip Erdogan confirmed that foreign tourists were among the casualties.
He said during a speech in Ankara that a Syria-linked suicide bomber was believed to be behind the blast.
"I strongly condemn the terror attack which was carried out by a suicide bomber of Syrian origin," Erdogan said.
There was no immediate claim of responsibility.
Turkey's Prime Minister Ahmet Davutoglu has convened an emergency security meeting of key ministers and officials.
Following the explosion, ambulances rushed to the site in Sultanahmet Square, close to the Blue Mosque and Hagia Sophia, in a major tourist area of Turkey's most populous city, ferrying away the wounded as police cordoned off streets.
Police are reportedly taking extra measures to protect people against the possibility of a second explosion.
Al Jazeera's Emre Rende, reporting from Istanbul, said information was scarce immediately after the blast.
"Witnesses have said that the blast was heard from other neighbourhoods," he said. "Witnesses said that the ground shook."
Rende said police were conducting searches outside the cordoned-off area in case a second bomber was involved.
Erdem Koroglu, who was working at a nearby office at the time of the explosion, told NTV television he saw several people lying on the ground following the blast.
"It was difficult to say who was alive or dead," Koroglu said. "Buildings rattled from the force of the explosion."
|Police are conducting searches outside the cordoned-off area in case a second bomber is involved [IHA via AP]|
The blast comes just over a year after a female suicide bomber blew herself up at a police station for tourists off the same square, killing one officer and wounding another.
Turkey has become a target for the Islamic State of Iraq and the Levant (ISIL), with two bombings last year blamed on the armed group, in the town of Suruc near the Syrian border and in the capital Ankara. The latter killed 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) armed group, which has been fighting for three decades for Kurdish autonomy.
Source: Al Jazeera and agencies