Pope Francis arriving to meet with South Korea's religious leaders at Myeong-dong Cathedral in Seoul yesterday. Photo: Jung Yeon-je/Reuters

Pope Francis said yesterday the international community would be justified in stopping Islamist militants in Iraq, but that it should not be up to a single nation to decide how to intervene in the conflict.

The leader of the world’s 1.2 billion Roman Catholics made his comments in an hour-long conversation with reporters aboard a plane returning from a trip to South Korea that ranged from international diplomacy to his health and future travel plans.

During the encounter that has become a tradition at the end of his foreign journeys, Francis, 77, also said he planned to visit the United States next year and that he was ready to go to China “tomorrow” if the communist government allowed him.

He said he realised he had to slow down and be more “prudent” with his health and that he had learned how to handle the super-star status he has gained since coming to office last year by thinking of his errors and his own imminent mortality.

Francis was asked if he approved of US strikes against Islamic State insurgents who have recently forced Christians and other minorities to flee their homes in Iraq.

“In these cases, where there is an unjust aggression I can only say that it is legitimate to stop the unjust aggressor,” he said.

Proclaiming a caliphate straddling Iraq and Syria, the militants have swept across northern Iraq, pushing back Kurdish regional forces and driving tens of thousands of Christians and members of the Yazidi religious minority from their homes.

The Pope was careful not to give the impression that he was giving an automatic green light for military strikes, but he did not rule them out.

He said the situation was grave and the international community had to respond together.

“I underscore the verb ‘to stop’. I am not saying ‘bomb’ or ‘make war’, but stop him [the aggressor]. The means by which he can be stopped must be evaluated. Stopping the unjust aggressor is legitimate,” he said.

“One single nation cannot judge how he is to be stopped, how an unjust aggressor is to be stopped,” he said.

He said the United Nations was the proper forum to consider whether there was unjust aggression and how to stop it.

The Pope disclosed that he had considered going to Iraq after his return from Korea, but decided against a visit for the time being. “At this moment, it would not be the best thing to do, but I am willing to do it,” he said.