"I appeal to the conscience of those responsible for the bombardment, who will have to answer before God," the pope said at his weekly address in St Peter's square, without naming Syria or Russia.
He spoke of his "deep pain and serious concern about the events" in Aleppo, where air strikes by Syrian and Russian forces on eastern rebel positions have sparked international condemnation.
The Pope referred to Aleppo as a "battered city where children, the elderly, the sick, the young, the old are dying... So many people."
The recent airstrikes have been some of the fiercest since the start of the five-year conflict in Syria.
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They followed last week's collapse of a ceasefire deal brokered by Washington and Moscow.
The pope's comments come two days after the US accused Moscow of "barbarism" over the carnage in Aleppo, where France said Tuesday that "war crimes" were being committed.
Some 140 people, nearly all civilians, have been killed in the Syrian and Russian raids since late Thursday.
Yesterday, the Syrian army took control of a rebel-held district in the centre of the city, its first advance since Damascus announced last week it would retake the whole of the divided city.