Pope Francis expressed deep sadness for the beheading of 21 Egyptian Coptic Christians in Libya, departing from the script of an address on Monday to emphasise the unity of all Christians regardless of the sect they follow.
Addressing members of the Church of Scotland, the Argentine pope mentioned the killings which took place on a beach in Libya and were filmed and broadcast on Sunday by a website that supports Islamic State.
"Their only words were: 'Jesus, help me!' They were killed simply for the fact that they were Christians," Francis said in his native Spanish, departing from the Italian he uses at most formal events.
The leader of the world's 1.2 billion Catholics, who has said it is "lawful" to stop an unjust aggressor, went on:
"The blood of our Christian brothers and sisters is a testimony which cries out be heard. It makes no difference whether they be Catholics, Orthodox, Copts or Protestants. They are Christians!"
Francis added: "The martyrs belong to all Christians."
Egypt, where Christians make up around a tenth of a predominantly Muslim population, is stepping up its battle against Islamist militants in neighbouring Libya.
The Coptic Church is founded on the teachings of St. Mark who took Christianity to Egypt during the reign of the Roman emperor Nero.