Roman Catholic cardinals from around the world will meet on October 20 to discuss the conflicts in Iraq and Syria where jihadist forces threaten Christians and other minorities, the Vatican said on Tuesday.

The meeting at the Vatican, known as a consistory, is the highest-level decision-making event that a pope can convene and usually deals with appointing new cardinals and considering dossiers for sainthood.

But Pope Francis, who last month described the jihadist upsurge as a "World War III in piecemeal", wants Middle East issues to top the agenda.

Vatican spokesman Federico Lombardi said the cardinals would review recommendations by papal ambassadors, or nuncios, to the region who met with Francis at the Vatican last month.

They called on the international community not to remain "inert" in the face of "the massacre of people solely because of their religious and ethnic affiliation", and spoke out against the "decapitation and crucifixion of human beings" as well as the destruction of places of worship and the displacement of thousands of people.

They also called for a "military response" as well as efforts to address the root causes of extremist ideology through dialogue and education.

A Franciscan priest and 20 other Christians were seized overnight Sunday by Al-Qaeda affiliate Al-Nusra Front in a village in northwestern Syria.