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Istanbul's Sultanahmet district hit by blast; at least 10 dead, 15 wounded

An explosion in a popular Istanbul tourist zone killed at least 10 people on Tuesday, officials said.

ISTANBUL — A suicide bomber linked to ISIS killed 10 foreigners and wounded 15 other people in a popular tourist area in Istanbul on Tuesday morning, Turkish officials said.

Turkish Prime Minister Ahmet Davutoğlu said the bomber who was a member of ISIS and that all those killed in the attack were foreigners. The attacker was described by the deputy prime minister as a Syrian national in his late 20s.

There was no immediately claim of responsibility for the attack, the latest in a string of deadly terror incidents to strike the nation.

Local Turkish media reported that the majority, if not all, of those killed in the blast dead were German nationals.

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

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 areas most popular with tourists.

Surrounding streets were closed off 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, and following the explosion there was a flood of activity on social media from people checking on their friends and family.

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

"It was one big blast, one massive blast … it sounded like something you only hear in the movies," Egbareia told NBC News by telephone.

He said he heard a woman screaming and ran to the door to see "three or four bodies" as well as the screaming woman, who was wounded, around 100 feet away.

Turkey is battling Kurdish militants and left-wing groups — along with the threat of ISIS-linked extremists.

A double suicide bombing blamed on ISIS killed more than 100 people in Ankara in October, and Turkey has since stepped up its efforts to tackle the militants.

Turkish officials in December said they had detained two suspected ISIS militants and foiled a plot to bomb the New Year's Eve celebrations in its capital, Ankara.

News of Tuesday's deadly attack prompted immediate condemnation from the international community.

"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."

British Foreign Secretary Philip Hammond called the blast "shocking" and the European Union's migration commissioner Dimitris Avramopoulos tweeted to "deplore and condemn the attack."

U.S. Ambassador to Turkey John Bass said: "Our thoughts are with those affected."

—NBC News' Alexander Smith and Richard Engel contributed to this article. 

This is a developing news story. Please check back for updates.