The powerful blast rocked the Sultanahmet neighborhood which is home to Istanbul’s biggest concentration of monuments and is visited by tens of thousands of tourists every day.
“Terrorist links are suspected,” a Turkish official told AFP, asking not to be named.
Ambulances and police were dispatched to Sultanahmet, which is home to world-famous monuments including the Blue Mosque and the Hagia Sophia, while police helicopters hovered above.
Prime Minister Ahmet Davutoglu convened an emergency security meeting of key ministers and officials, including powerful Interior Minister Efkan Ala and spy chief Hakan Fidan.
Turkey has been on high alert after a series of attacks blamed on the ISIS terrorist group including a double suicide bombing in the capital Ankara in October that left 103 people dead.
The Istanbul governor’s office said in a statement quoted by the Dogan news agency that 10 people were killed and 15 wounded in Tuesday’s blast.
“Investigations into the cause of the explosion, the type of explosion and perpetrator or perpetrators are under way,” the governor’s office said.
Images published by Dogan showed several apparently dead bodies lying on the ground.
The identities of those killed and hurt were not immediately clear although unconfirmed reports said the injured included two Germans and one Norwegian tourist.
Germany warned its nationals to avoid tourist sites in Istanbul, a city of about 14 million people that has been hit several times in the past by deadly attacks.
Media reports said the authorities were studying the possibility Tuesday's blast was caused by a suicide bomber but there was no official confirmation, AFP reported.
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