Yemeni security forces gather outside an elderly care home after it was attacked by gunmen in the port city of Aden, Yemen, March 4, 2016.

Gunmen opened fire and shot dead 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, took place in the restive district of al-Mansoura which has witnessed several assaults on local security officials.

Iran-allied Houthi rebels have forced Yemen’s embattled government out of the capital Sanaa. Yet, despite it being based in Aden now, the legitimate government is fighting to impose its authority even there.

Local officials and medical sources also stated on Friday that gunmen attacked an old people’s home in the Yemeni port of Aden, killing at least 15 people, including four Christian nuns from India.

After being one of the world’s busiest ports as a hub of the British Empire, the southern city has transformed into a backwater and then in recent months into a conflict zone.

A Saudi-led coalition began a military campaign a year ago to avert the Houthis plot to take complete control of Yemen.