Pope Francis has urged prayer for Catholic and Orthodox priests and bishops held prisoner by extremists in Syria.

Speaking before the midday Regina Caeli prayer in St Peter's Square, Francis referred to five priests killed during the Spanish Civil War, who were proclaimed saints the previous day. According to the Zenit news service, he said: "We praise the Lord for these courageous witnesses of His, and through their intercession we pray for the world to be liberated from all violence."

Francis continued: "Always alive in me is my concern for brother Bishops, priests and Religious, Catholics and Orthodox, kidnapped for a long time in Syria. May the Merciful God touch the heart of the abductors and grant the release of our brothers, to be able to return to their communities as soon as possible. Therefore, I invite you all to pray, without forgetting the other persons kidnapped in the world."

Among those held prisoner in Syria are two Orthodox bishops, kidnapped just over two years ago. Syriac Orthodox Metropolitan Gregorios Yohanna and Greek Orthodox Metropolitan Boulos Yazii, both from Aleppo, were kidnapped three years ago on April 22 near the city. Catholic priest Fr Jack Mourad was captured last year but released, while Fr Tom Uzhunnalil was kidnapped in Yemen after an attack on the old people's home where he was ministering and is thought to be still in the country.

Addressing an audience of young people at a Youth Jubilee celebration, Francis concluded: "Dear young people, you have celebrated the Jubilee: now you go home with the joy of your Christian identity. Standing, with your head held high, and with your identity card in your hands and in your heart! May the Lord accompany you, and please, pray also for me."