At least 15 people were killed on Sunday when a suicide bomber blew himself at a checkpoint in the southern city of Aden. At least 20 people were wounded in the attack, residents and a security official said. The ISIS terrorist organization later claimed responsibility for the attack. The attack occurred outside the main security headquarters in Aden’s Khor Maksar district, according to Aden residents and the security official. The blast was heard across the city and a plume of smoke could be seen from miles away. Clashes erupted in the area immediately afterward, witnesses reported. It was unclear who was behind the attack or the clashes that followed. ISIS said at least 50 people had been killed by the blast and in clashes. Al-Qaeda in the Arabian Peninsula (AQAP), the local branch of the global the extremist network, has been the most active group in southern Yemen in recent years. Aden is the interim headquarters of Yemen’s internationally recognized government, which had to move there when Houthi rebels took control of the capital, Sana’a, in 2015 during Yemen’s civil war.