A priest kidnapped in Syria a month ago has been released but others are still missing.

Father Tony Boutros, 50, a Melkite-Catholic priest, was taken by unknown assailants on July 12 when he was being driven to Mass. His driver was also kidnapped.

Patriarch Gregory III Laham, Patriarch of Antioch, disclosed the release of Father Boutros.

Still missing are Italian Jesuit Father Paolo Dall'Oglio and two Orthodox Archishops, Yohanna Ibrahim and Boulos Yazigi.

Not all kidnappings are by Islamic State and the terror group did not claim responsibility for Father Boutros. According to reports, Christian clergy have become almost a form of "currency" in the region, and in some cases a ransom has been paid to secure a release. There are many extremist factions and groups using what methods they can to raise money and seize power.

Earlier in July, Father Dhiya Aziz, a Franciscan priest from Iraq serving in north-west Syria, was kidnapped and freed five days later.

Pope Francis has called for an immediate end to the "genocide" of Christians in the Middle East, describing it as a "third world war".

He said recently: "We are dismayed to see how in the Middle East and elsewhere in the world many of our brothers and sisters are persecuted, tortured and killed for their faith in Jesus. In this third world war, waged piecemeal, which we are now experiencing, a form of genocide is taking place, and it must end."

John Newton, of Aid to the Church in Need, told the Christian Post. "I know of one priest who was kidnapped for two months. They asked for a ransom of $120,000, which the family managed to raise and deliver. But hours later, the priest was killed and his body cut up, with pieces of him sent in a box to the family."