Pope Francis said on Sunday that equating Islam with violence was wrong and called on Muslim leaders to issue a global condemnation of terrorism.

Francis, the leader of 1.2 billion Roman Catholics, told reporters aboard his plane returning from a visit to Turkey that he understood why Muslims were offended by many in the West who automatically equated their religion with terrorism.

Francis' predecessor, Benedict XVI, caused storms of protest throughout the Islamic world in 2006, when he made a speech that suggested to many Muslims that he believed Islam espoused violence.

Benedict said he had been misunderstood and apologized. But this year, the image of a violent religion has once more been promoted by Islamic State, who have seized swathes of Syria and Iraq, slaughtering or driving out Shi'ite Muslims, Christians and others who do not share their radical brand of Sunni Islam.

The Argentine pope, who has been trying to foster cooperation with moderate Islam in order to work for peace and protect Christians in the Middle East, said it was wrong for anyone to react to terrorism by being "enraged" against Islam.

"You just can't say that, just as you can't say that all Christians are fundamentalists. We have our share of them [fundamentalists]. All religions have these little groups," he said.

"They [Muslims] say: 'No, we are not this, the Koran is a book of peace, it is a prophetic book of peace'."

Francis said he had made the suggestion of a global condemnation of terrorism by Islamic leaders in talks on Friday with Turkish President Tayyip Erdogan.

"I told the president that it would be beautiful if all Islamic leaders, whether they are political, religious or academic leaders, would speak out clearly and condemn this because this would help the majority of Muslim people," he said.

Francis several times condemned Islamic State's insurgents during his three-day trip. On the plane, he said some Christians had been forced to abandon everything: "They are driving us out of the Middle East."

In an address at a Mass on Sunday, he said Islamic State were committing a "profoundly grave sin against God" and called for inter-religious dialogue and action against poverty to help end the conflicts in the region.

He added that ending poverty was crucial, partly because it gave rise to "the recruitment of terrorists". Francis has in the past said that, while it is lawful for the international community to use force to stop an "unjust aggressor", lasting solutions must be found that tackle the root causes of violence.