Story highlights Gunmen burst into a home, handcuffed people, then shot them in the head, Vatican says

Pope "prays that this pointless slaughter will awaken consciences" and spur peace talks

Yemen has been beset by violence for years, with U.N. estimating up to 2,800 civilian deaths

(CNN) There are few places in Yemen -- homes, schools, hospitals -- that haven't been scarred by the ongoing war ravaging that Arab nation.

And now, a home for the elderly run by Catholic missionaries is among them.

The Vatican on Saturday reported the killing of four Missionaries of Charity members plus 12 others at an elderly facility in the port city of Aden.

According to an official Vatican News report , gunmen burst into the building Friday, went room to room handcuffing victims, then shot all 16 in the head.

Aden is on Yemen's southern coast, across the Gulf of Aden from Somalia.

Agenzia Fides , an information service for Catholic missionaries, reported the missionaries -- who belonged to the group founded by Mother Teresa -- were nuns. Two were from Rwanda, one from India and the fourth from Kenya.