Smoke billows following an airstrike by the Saudi-led coalition May 11, 2015, in Yemen's capital of Sanaa. Mohammed Huwais/AFP/Getty Images

Gunmen opened fire and killed a police colonel and his aide as their vehicle was passing through a roundabout in the southern Yemeni city of Aden on Saturday, a local security official and witnesses said.

The attack on Col. Salem al-Milqat, police chief of Tawahi district, occurred in the restive district of al-Mansoura, which has seen several assaults on local security officials.

Yemen’s embattled government has been forced out of the capital by Iran-allied Houthi rebels and is now based in Aden but struggles to impose its authority even there.

Gunmen Friday attacked an old people’s home in the Yemeni port of Aden, killing at least 15 people, including four Christian nuns from India, local officials and medical sources said.

The southern city has gone from being one of the world’s busiest ports as a hub of the British empire to a backwater and then in recent months to a conflict zone.

A Saudi-led coalition began a military campaign a year ago to prevent the Houthis from taking complete control of Yemen.