A suicide car bomber blew himself up at a security checkpoint in the southern Yemeni port city of Aden on Sunday, killing 15 people and wounding at least 20, residents and a security official said.

Islamic State claimed responsibility for the assault, without providing evidence.

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.

Islamic State claimed responsibility for the attack in a statement posted on the internet, though without immediate evidence to back up its assertion. IS 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 Islamist militant network, has been the most active jihadist 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, Sanaa, in 2015 during Yemen’s civil war.

More than 10,000 people have been killed in the conflict since the Houthis advanced on Aden , forcing President Abd-Rabbu Mansour Hadi to flee and seek help from Saudi Arabia.

Aden is dominated by Yemeni forces backed by the United Arab Emirates, a key member of the Saudi-led coalition that intervened in Yemen’s war to restore Hadi.

Saudi Arabia’s air defense forces intercepted a ballistic missile fired from Yemen over the capital, Riyadh, on Saturday, state news agencies reported.

The missile was brought down near King Khaled Airport on the northern outskirts of the city and did not cause any casualties.