Pope Francis has written to Iraqi President Fouad Massoum, urging him to put an end to the "brutal suffering" of religious minorities at the hands of the Islamic State (IS).

Delivered by the Pope's envoy to Iraq, Cardinal Fernando Filoni, the letter from Francis reads: "I appeal to you with my heart full of pain while I follow the brutal suffering of Christians and other religious minorities who are forced to leave their homes, as their places of worship are destroyed."

The Pontiff has called for immediate intervention and an increase in humanitarian aid for those suffering in Iraq.

He previously wrote to UN Secretary General Ban Ki-Moon, urging for the implementation of humanitarian laws to eradicate "systematic violence against ethnic and religious minorities".

Noting his "heavy and anguished heart", the Pope expressed a concern "for the intolerable suffering of those who only wish to live in peace, harmony and freedom in the land of their forefathers".

He urged the UN to use its full resources to provide humanitarian assistance in Iraq, declaring: "The violent attacks that are sweeping across Northern Iraq cannot but awaken the consciences of all men and women of goodwill to concrete acts of solidarity by protecting those affected or threatened by violence and assuring the necessary and urgent assistance for the many displaced people as well as their safe return to their cities and their homes.

"The tragic experiences of the Twentieth Century, and the most basic understanding of human dignity, compels the international community, particularly through the norms and mechanisms of international law, to do all that it can to stop and to prevent further systematic violence against ethnic and religious minorities," he concluded.

Francis has been vocal about the crisis in Iraq since its beginning, and on Sunday offered a surprising endorsement of military action against Islamic insurgents.

Asked whether he thought US military strikes were justifiable, the Pope replied: "In these cases, where there is an unjust aggression I can only say that it is legitimate to stop the unjust aggressor.

"I underscore the verb 'to stop'," he continued. "I am not saying 'bomb' or 'make war', but stop him. The means by which he can be stopped must be evaluated. Stopping the unjust aggressor is legitimate."

He also revealed that he had considered travelling to the fractured region himself, but "At this moment, it would not be the best thing to do.

"But I am willing to do it," Francis said.

Furthermore, the 77-year-old Pontiff apparently phoned murdered US journalist James Foley's family on Thursday to offer his personal condolences.

Vatican spokesman Federico Lombardi said Francis called to "console them for their loss and assure them of his prayers".

The family were said to be "deeply grateful and moved by the Pope's gesture".

A video was released by IS on Tuesday, showing Foley being beheaded by a man thought to be a British jihadist.