An explosion in the heart of Istanbul’s historic Sultanahmet tourist district killed at least ten people and wounded 15 on Tuesday and some local media reports said a suicide bomber may have been responsible.

Several bodies lay on the ground in the Sultanahmet square, close to the Blue Mosque and Hagia Sophia, a major tourist area of Turkey’s most populous city. A police officer and witness at the scene reported also seeing several bodies and body parts.

Six German citizens, one Norwegian and one Peruvian were among the wounded, the Dogan news agency said.

A tour company official told Reuters a group from Germany was in the area at the time but said there was no immediate information on whether any of them had been injured.

An official at the German foreign ministry said it could not be ruled out that German citizens may have been injured and that its crisis unit and the consulate in Istanbul were urgently working with the Turkish authorities to find out.

Norway’s foreign ministry said one Norweigan man was injured and was being treated in hospital.

The attack at the heart of one of the world’s most visited cities comes as Turkey battles Kurdish militants in its southeast and Islamic State insurgents just across its southern borders in Syria and Iraq.

There was no immediate claim of responsibility but Islamist, leftist and Kurdish militants have all carried out attacks in Turkey in the past.

The Istanbul governor’s office said the authorities were investigating the type of explosive used and who might have been responsible. It said ten people were killed and 15 wounded but gave no further details.

“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.

A police officer at the scene said the square was not densely packed at the time of the blast, but that small groups of tourists were wandering around.

“It was unimaginable,” he said, describing an amateur video he had seen of the immediate aftermath, with six or seven bodies lying on the ground and other people seriously wounded.

Turkey’s AHaber television said the blast may have been caused by a suicide bomber but this was not independently confirmed. Ambulances rushed to the scene, ferrying away the wounded as police cordoned off streets, fearing a second attack.

“The explosion was very loud. We shook a lot. We ran out and saw body parts,” one woman who works at a nearby antiques store told Reuters, declining to give her name.

‘Terrorist Links’ Suspected

Prime Minister Ahmet Davutoglu held an emergency meeting in Ankara with the interior minister and security chiefs. A senior official said “terrorist links” were suspected in the attack, but declined to comment further.

The dull thud of the explosion was heard in districts of Istanbul several kilometers away, residents said. Tourist sites including the Hagia Sophia and the nearby Basilica Cistern were closed on the governor’s orders, officials said.

The sound of the call to prayer rang out from the Blue Mosque as forensic police officers worked at the scene.

Just over a year ago, a female suicide bomber blew herself up at a police station for tourists off the same square, killing one officer and wounding another. That attack was initially claimed by a far-left group, but officials later said it had been carried out by a woman with suspected Islamist militant links.

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.

The PKK has however generally avoided attacking civilian targets in urban centers outside the southeast in recent years.

“Ambulances started rushing in and I knew it was a bomb right away because the same thing happened here last year,” said Ali Ibrahim Peltek, 40, who operates a kiosk selling snacks and drinks on the square.

“This is not good for Turkey but everyone was expecting a terrorist attack,” he said.

Davutoglu’s office imposed a broadcasting ban on the blast, invoking a law which allows for such steps when there is the potential for serious harm to national security or public order.

(Additional reporting by Ece Toksabay in Ankara, Humeyra Pamuk and Daren Butler in Istanbul, Madeline Chambers in Berlin; Writing by Nick Tattersall; Editing by Philippa Fletcher)

Tags: istanbul, security, unrest

Photo credit: Police secure the area after an explosion near the Ottoman-era Sultanahmet mosque, known as Blue mosque in Istanbul, Turkey January 12, 2016. Murad Sezer / Reuters