Father Paolo Dall'Oglio, a Jesuit priest who worked in Syria for more than 30 years and who supported the uprising against President Bashar al Assad, disappeared on July 29, 2013 in the city of Raqqa, now a stronghold of militant group Islamic State.Dall'Oglio was well known in the Middle East and Europe for his work promoting Christian-Muslim dialogue. He was restoring an ancient monastery in the desert and had refused to leave the country for his own safety after the civil war started four years ago.Several months earlier, two Orthodox bishops were kidnapped in an area near the Turkish border where they had gone to negotiate the release of two abducted priests.Francis, speaking to tens of thousands of people in St. Peter's Square for his weekly prayer and message, called for a "renewed commitment" by local and international authorities "so these brothers of ours can regain their freedom soon."More than a quarter of a million people have been killed since the civil war in Syria began, and many have been abducted or are missing.Syrian President Bashar al Assad said on Sunday the army had been forced to give up areas in order to hold onto more important ones in its fight with insurgents.