Gunmen suspected of being from the local ISIS affiliate attacked a nursing home in the southern Yemen port city of Aden today, killing 17 people, four of them nuns who worked at the facility, originally founded by Mother Theresa.

There was no apparent motive for the attack, but officials noted that the 60 residents at the facility were not harmed. The dead included nuns, guards, and the gardener who worked at the site. The Yemeni mission to the UN blasted it as a “cruel and heartless act,” and suggested it was likely an ISIS operation.

Neither ISIS nor anyone else has claimed responsibility for the attack, however the fact that the site is run by Christians is something that might conceivably encourage ISIS to launch such an attack.

Local accounts suggested the attackers were disguised as visitors, and captured and tied up the staff at the site in a room before executing them all. None of the gunmen was captured in the attack. Aden is the “interim” capital city of pro-Saudi forces in Yemen, and has seen a growing number of Islamist attacks in recent weeks.