An eyewitness account has emerged describing the terror faced by the four nuns from Mother Teresa's order murdered by Islamic State in Yemen on March 4.

A fifth nun, Sister Sally, who escaped after she hid in a refrigerator, wrote a memo to another member of the order, Sister Rio, about the 90 minutes of terror, in which a further 12 people were also slain.

The memo, obtained by news site Crux, reports that on that Friday, the sisters had said Mass and had breakfast as usual. At 8am the priest said the apostolate prayer and all five nuns went to the home where about 80 elderly and disabled people live.

Shortly after, terrorists from Islamic State, dressed in blue, entered the premises and began killing, starting with the guard. Five young Ethiopian Christian men ran to tell the sisters that Islamic State was there to kill them. The men were caught, tied to trees, shot in the head and then had their heads smashed in. 

The sisters ran for their lives, and four other women who worked there shouted: "Don't kill the sisters! Don't kill the sisters!" These four women were murdered as well. One had been the cook for 15 years. 

Sister Sally ran to the convent to try to warn Salesian priest Fr Uzhunnalil, who is still missing after being kidnapped by the terrorists. Instead of fleeing, he ran to the chapel and consumed all the consecrated hosts so the terrorists could not defile them. After capturing the priest, they went on a destructive anti-Christian hate-filled rampage, destroying every other religious item, including the tabernacle, altar, crucifix and an image of the Virgin Mary.

Two of the murdered sisters were from Rwanda, one was from India and one from Kenya. 

The attack provoked outrage around the world, and the pope and his staff in Rome are among those who have prayed for those involved, with their concerns going viral on social media. 

Yemen is on the southern edge of the Arabian Peninsula and is currently gripped by civil war.

More than 6,000 people have been killed and 28,500 people injured, according to the United Nations.

The Missionaries of Charity was founded in 1950 by Mother Teresa, who is to be made a saint this autumn.

The Apostolic Vicariate of Southern Arabia has said the murdered nuns were all serving the poor, whatever their religion, and saw this as their duty.

Pope Francis has described them as "martyrs of today who gave their blood for the Church."