In his traditional Easter message, the 78-year-old pontiff prayed that the framework accord reached Thursday between Iran and six major world powers would be "a definitive step toward a more secure and fraternal world."
Tens of thousands of pilgrims huddled under umbrellas in a rain-soaked St. Peter's Square to hear the pope deliver his "Urbi et Orbi" (To the City and World) blessing, broadcast live to dozens of countries.
Speaking from the balcony of St Peter's Basilica, Francis urged prayers for those killed in armed conflict, saying: "I think in particular of the young people who were killed last Thursday at Garissa University College in Kenya," referring to the attack by Somali Shebab extremists that left 148 people dead.
In his third Easter address since his election as pope in 2013, the head of the world's 1.2 billion Catholics prayed "for peace, above all, for Syria and Iraq, that the roar of arms may cease".
He called on the international community to "not stand by before the immense humanitarian tragedy unfolding in these countries and the drama of the numerous refugees" created by the two conflicts.
The Argentine pope also pleaded for "absurd bloodshed and all barbarous acts of violence" in Libya to be halted, and voiced his "desire for peace, for the good of the entire people" in war-battered Yemen and Ukraine.
Be 'respectful, ready to help'
He prayed for "all who have been kidnapped, and for those forced to abandon their homes and their dear ones" in armed conflict and attacks by extremists in Nigeria and South Sudan as well as parts of Sudan and the Democratic Republic of the Congo.
In addition, he urged "peace and freedom for the many men and women subject to old and new forms of enslavement on the part of criminal individuals and groups... for the victims of drug dealers... And we ask peace for this world subjected to arms dealers."
Francis also sounded his trademark appeal to the rich and powerful to care for the world's poor and downtrodden, saying: "The world proposes that we put ourselves forward at all costs, that we compete."
Instead, Christians should "seek to live in service to one another, not to be arrogant, but rather respectful and ready to help," he said.
Sunday's Easter observances capped a long and demanding Holy Week that left Francis at times appearing tired.
On Friday he presided over the traditional Via Crucis (Way of the Cross) procession at Rome's Colosseum evoking the last hours of Jesus's life.
The day before Francis celebrated two masses -- one for priests, and the other at Rome's Rebibbia prison, where he washed the feet of 10 inmates symbolically evoking Christ's humility -- a theme he took up again on Sunday.
"To enter into the mystery, we need to 'bend down', to abase ourselves," Francis said.