Francis made similar comments when he was archbishop of Buenos Aires but his remarks to reporters on a plane returning from a Middle East trip were the first he has made since becoming pope.

"Celibacy is not a dogma," he said in answer to a question about whether the Catholic Church could some day allow priests to marry as they can in some other Christian Churches.

"It is a rule of life that I appreciate very much and I think it is a gift for the Church but since it is not a dogma, the door is always open," he said.

The Church teaches that a priest should dedicate himself totally to his vocation, essentially taking the Church as his spouse, in order to help fulfill its mission.