The Mother Teresa sisters killed in Aden knew the risks they faced in remaining in the country, according to the Catholic Vicar Apostolic for Southern Arabia.

The four nuns were killed when gunmen stormed a Catholic-run retirement home in Yemen's southern city, killing 16 people. A priest was taken captive and is still missing.

The home, run by the Missionaries of Charity, an organisation established by Mother Teresa of Calcutta, has about 80 residents.

Bishop Paul Hinder told the Fides news agency he had discussed the volitile situation in Yemen with the sisters about a year ago. "They told me there was nothing to discuss: they would not leave whatever happened, because they wanted to stay with the people entrusted to their care. It was clear that on the part of the sisters this was no exhibition of heroism, it was purely their desire to follow Jesus Christ. I respected the sisters' decision, and am convinced that their martyrdom will bear fruit also for the lives of other Christians living in the Arabian peninsula".

Hinder said the local people loved the sisters and admired their selfless service. "This earned the Sisters the people's warmth and affection and perhaps that was precisely what some disliked," he said.

In a sign of the insecurity in Aden, jihadists raided a school yesterday and gave a "last warning" to students who had not complied with a dress code ordering women to adapt their clothing to comply with Islamic law. A leaflet was circulated threatening death to Jews, Christians and 'infidels' who breached it. "We will kill anyone who violates the law of God," the leaflet said.