Pope Francis called on Monday for collective action through the United Nations to "stop unjust aggression" in Iraq, in an implicit criticism of unilateral US air strikes against Islamic militants there.
Asked about recent US strikes against Islamic State targets in northern Iraq, the pope said that "in the case where there is unjust aggression, it is acceptable to stop an unjust aggressor. I emphasise the word 'stop'. I am not saying 'bombard' or 'make war upon'."
"One nation cannot decide" alone how to end the aggression, the pontiff, speaking aboard the flight bringing him back from a trip to South Korea, added.
"The idea of the United Nations came after the Second World War. That is where we should be having the discussion and saying, 'there is an unjust aggressor. How are we going to stop it?'"
Last week, after thousands of Iraqi Christians had fled attacks by Islamic State jihadists in the north, Francis made a plea to the UN to do all it can to stop the violence.
The Holy See's ambassador to the United Nations, Silvano Tomasi, voiced support days earlier for the US air strikes, in a notable rare exception to Vatican policy promoting peaceful conflict resolution.
"Military action might be necessary," Tomasi said.
Francis told reporters on Monday he was glad to be able to clarify his position on the right to a legitimate defence in the face of the risk of genocide.
Church figures on the ground in Iraq, where the Islamic State and other militant groups are carrying out a brutal offensive, have warned that Christian persecution may be becoming a genocide.