A square was rocked by an explosion in the center of the historical Sultanahmet tourist district in Istanbul on Tuesday and witness and a police officer in the scene reported seeing body parts following the blast.

Ambulances raced in an important tourist area of Turkey’s most populous city, ferrying the wounded away as police cordoned off roads, close to the Blue Mosque and Hagia Sophia.

“We are taking precautions against another explosion,” the police officer said, ushering people from the square.

The AHaber television in Turkey said the blast could have been due to a suicide bomber but this wasn’t independently verified. The explosion was quite loud. A lot shook.

Kurdish, Islamist and leftist militants all have carried out attacks in Turkey before.