Updates To Istanbul Explosion As Turkish Authorities Confirm Rising Death Toll

According to Turkish authorities, at least 10 people were killed in an explosion that rocked Istanbul's historic Sultanahmet district Tuesday morning. Another 15 people were injured in the attack, the Istanbul governor's office said in a statement on its website. "Investigations continue about the explosion's cause, the explosive's types, the perpetrator/perpetrators of the event," Istanbul Gov. Vasip Şahin said in the post.

Hours after the explosion, Turkish President Recep Tayyip Erdoğan said a Syrian suicide bomber was believed to have been responsible. As of midday Tuesday, however, no one claimed responsibility for the attack.

Videos and photos posted online showed emergency services rushing to the area following the explosion. The identity and nationalities of the victims were also not immediately disclosed, though CNN Turkey reported that tourists from Germany, Norway, and Peru were among the injured. According to the Associated Press, six Germans, one Norwegian, and one Peruvian were injured.

The explosion took place a little after 10 a.m. local time in the heart of Sultanahmet, a popular tourist destination with many historic landmarks, including the Blue Mosque and Hagia Sophia. The square already commands a heavy police presence due to mounting security threats in the country. Though the immediate scene was cordoned off, photos posted on social media seemed to indicate that other areas of the city were still bustling with visitors.

Turkey serves as a key, though testy, U.S. ally in the Middle East region. Its southern border lies against Syria and Iraq, both of which house ISIS and other terrorist groups, and that violence has begun to bleed over into Turkey. In October, two suicide bombers suspected of having ISIS connections detonated during a peace rally in Ankara, killing more than 100 people and injuring hundreds more. According to Reuters, Kurdish, leftist, and Islamist groups have all exerted violence in the country before.