Gunmen stormed a retirement home run by a Roman Catholic charity in southern Yemen, killing more than a dozen people, including four nuns.
A spokesman for the Missionaries of Charity, which ran the home in the port city of Aden, said four of the gunmen entered the building on the pretext they wanted to visit their mothers.
A Yemeni official said the gunmen then moved from room to room, handcuffing the victims before shooting them in the head.
The motive of the gunmen, who fled after the attack, was not immediately clear.
Yemen's embattled government is based in Aden but has struggled to impose its authority there since its forces, backed by Gulf Arab troops, expelled Houthi fighters who still control the country's capital, Sanaa.
The Missionaries of Charity is an organization established by Mother Teresa, the renowned Nobel Prize winning nun who died in 1997.