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Jan. 12, 2016, 8:49 AM GMT / Updated Jan. 12, 2016, 6:30 PM GMT By Aziz Akyavas, Alexander Smith, Richard Engel and Cassandra Vinograd

ISTANBUL — An ISIS suicide bomber killed 10 people and wounded 15 more Tuesday when he set off a deadly blast in the heart of Istanbul, Turkish officials said.

The attacker was a Syrian national in his late 20s and all his victims were foreigners, Turkish Prime Minister Ahmet Davutoğlu said.

Local media reported that the majority, if not all, of those killed in the explosion were German.

The German government would not confirm those reports but said their nationals were among those affected by the blast and the possibility of casualties could not be excluded.

"Today Istanbul was hit; Paris has been hit, Tunisia has been hit, Ankara has been hit before," German Chancellor Angela Merkel told a news conference. "International terrorism is once again showing its cruel and inhuman face today."

Ömer Taşpınar, a professor of National Security Strategy at the U.S. National War College in Washington, said Turkey's economy may have been a target.

“With tourism revenues affected, Turkey will pay a heavy financial price,” he said.

Tuesday's explosion struck close to a monument called the German Fountain, between the Blue Mosque and the Haghia Sofia — the city's famous landmark-turned-museum and one of Istanbul's most popular tourist destinations.

Surrounding streets were closed by authorities in the aftermath and many shops and hotels appeared to have shut their doors. Armed officers and riot police guarded a wider perimeter.

The blast could be heard for miles across the city. After the explosion, there was a flood of activity on social media as worried people checked on the fates of their friends and loved ones.

Majd Egbareia, a 28-year-old nurse from Israel on vacation with his family, was praying in the nearby Blue Mosque when the blast shook the square.