A 28-year-old Syrian national blew himself up in a popular tourist district of Istanbul Tuesday, killing at least 10 people and injuring at least 15 more, Turkish government officials said.

Turkey’s Dogan news agency reported that at least six Germans, one Norwegian and one Peruvian were among the wounded, and Seoul’s Foreign Ministry told reporters via text message that one South Korean had a finger injury. The Norwegian Foreign Ministry told Norway’s news agency NTB that the Norwegian tourist was slightly hurt and was being treated in a local hospital.

Authorities in Germany and Denmark warned citizens visiting Turkey to avoid crowds outside tourist attractions in Istanbul. German officials said on a government website that further violent clashes and “terrorist attacks” are expected across Turkey. Germany also urged travelers to stay away from demonstrations and gatherings, particularly in large cities.

The explosion, which could be heard from several neighborhoods, was at a park that is home to a landmark obelisk, some 25 yards from the historic Blue Mosque.

Sultanahmet is Istanbul’s main sightseeing area and includes the Topkapi Palace and the Haghia Sophia museum.

A government official, speaking on condition of anonymity because of government rules, told the Associated Press the explosion was believed to be “terror-linked”.

Omer Celik, the spokesman for Prime Minister Ahmet Davutoglu’s ruling party issued a statement condemning what he called “a heinous attack.” Davutoglu convened a security meeting immediately following the explosion with the country’s interior minister and other officials.

As with previous attacks, authorities imposed a news blackout, barring media from showing images of the dead or injured or reporting any details of the investigation.

Police sealed the area of the explosion, barring people from approaching in case of a second explosion and a police helicopter hovered overhead

The explosion was set off at approximately 10:20 a.m. local time, according to the Hurriyet newspaper. 

Erdem Koroglu, who was working at a nearby office at the time of the explosion, told NTV television he saw several people lying on the ground following the blast.

“It was difficult to say who was alive or dead,” Koroglu said. “Buildings rattled from the force of the explosion.”

Turkey suffered two major bombing attacks last year.

More than 30 people were killed in an ISIS suicide attack in the town of Suruc, near Turkey’s border with Syria, in July.

Two suicide bombs in October outside Ankara’s main train station as people gathered for a peace rally killed more than 100 people. It was Turkey’s deadliest attack. The prosecutor’s office said the attack was carried out by a local ISIS cell.

Last month, Turkish authorities arrested two suspected ISIS militants they said were planning suicide bombings during New Year’s celebrations in the capital.

The Associated Press contributed to this report.

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