Pope Leo made an impassioned plea on Sunday for an immediate ceasefire in the expanding Iran war, lamenting "atrocious violence" that he said had killed thousands of non-combatants and caused suffering across the region.

As the US-Israeli war on Iran enters its third week, the first US pope warned that violence would not bring the justice, stability, and peace that the peoples of the region long for.

"For two weeks, the peoples of the Middle East have been suffering the atrocious violence of war," the pope said at his weekly Angelus prayer in St. Peter's Square.

"In the name of Christians in the Middle East and of all women and men of good will, I appeal to those responsible for this conflict: Cease fire!" Pope Leo said.

Leo added that the situation in Lebanon - ravaged by a war between Israel and the Iran-backed Lebanese group Hezbollah - was also a cause of "great concern."

"I hope for paths of dialogue that can support the country's authorities in implementing lasting solutions to the serious crisis currently underway, for the common good of all the Lebanese people," the pope said.

During a visit to a Rome parish later, the pope said war could never resolve problems and hit out at people who invoke God to justify killings.

"Today, many of our brothers and sisters in the world are suffering because of violent conflicts, caused by the absurd claim that problems and disagreements can be resolved through war, when instead we must engage in unceasing dialogue for peace," he said during his homily.

"Some even go so far as to invoke the name of God to justify these choices of death, but God cannot be enlisted by darkness. Rather, He always comes to bring light, hope, and peace to humanity."