“The world is at war, the world is suffering,” the Argentine pontiff said ahead of the meeting, which came as fighting resumed in Syria and US authorities investigated an attack possibly linked to the Islamic State group.
“There is no God of war,” he said, calling on “all men and women of good will, of any religion, to pray for peace”.
The annual World Day of Prayer event, established by John Paul II 30 years ago and held in the medieval town of Assisi in central Italy, aims to combat extremism dressed up as religion and the persecution of people for their faiths.
The pope also reminded Western countries that while they had suffered a string of deadly jihadist attacks, there were parts of the world where cities were being flattened by fighting, prisoners were being tortured and families were starving to death.
“We are frightened… by some terrorist acts,” he said during morning mass at the Vatican, “(but) this is nothing compared to what is happening in those countries, in those lands where day and night bombs fall.”
“As we pray today, it would be good if we all felt shame, shame that humans, our brothers and sisters, are capable of doing this.”
The pope held one-on-one talks with faith leaders, including the Archbishop of Canterbury Justin Welby, the Orthodox Patriarch of Constantinople Bartholomew I, and Din Syamsuddin, chairman of Muhammadiyah, Indonesia’s second largest Islamic organisation.
Rabbi David Rosen, from the American Jewish Committee and Koei Morikawa, the Supreme Head of the Tendai Japanese school of Mahayana Buddhism, also met Francis.
The 79-year-old pope had arrived amid tight security in Assisi for lunch with the leaders and a group of refugees, including Syrians and Palestinians, an Eritrean, two Nigerian women and a 23-year-old from Mali who fled crisis-torn Libya for Sicily by boat.
The meal was rounded off with a cake sporting 25 candles to celebrate Bartholomew I’s 25 years as Patriarch, Italian media said.
At 4pm (1400 GMT) the leaders will pray before coming together for a joint ceremony where messages of peace will be read out by each leader and one of the war victims.
Some 500 representatives from different religious traditions have been taking part in a series of round-tables with lay people in the town since Sunday, covering topics from religious violence to climate change and the migration crisis.
It is the pope’s second visit in as many months to the picturesque hillside town, where his name-sake Saint Francis of Assisi was born and found God, renouncing his wealth for a life of poverty and becoming an emissary of peace.
The head of the world’s 1.2 billion Roman Catholics, who took the papal name Francis in homage to the famous Christian friar and his devotion to peace and forgiveness, has insisted violence committed in the name of religion has nothing to do with God.
During a trip to Poland in August he said “the world is at war”, but driven by greed for “interests, money, resources, not religion”.
“All religions want peace, it’s the others who want war”, he said, warning against equating Islam with terrorism, insisting there were fundamentalist Catholics too.