Updated | Tourists among those killed in Istanbul bomb blast

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.

Al Jazeera reports that most of those who were killed were foreigners. Meanwhile, at least two of those injured are in "critical condition".

"Investigations into the cause of the explosion, the type of explosion and perpetrator or perpetrators are under way," the governor's office said in a statement quoted by the Dogan news agency.

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. But authorities confirmed that the suicide bomber is a 28-year-old Syrian national. 

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.

Police cordoned off the area to protect people against the possibility of a second explosion.