The pope is "obviously very concerned about the hundreds of thousands of people who have been killed and wounded and the innocent civilian lives that have been lost", Milley told journalists aboard a US military aircraft following the audience.

"He's very interested in hearing my views on the state of the war and the status of the war, and the human tragedy that's unfolded in Ukraine," the general said.

Milley -- the chairman of the US Joint Chiefs of Staff -- has played a central role in efforts to provide Ukraine with assistance including military equipment and training to combat Russian troops who invaded in February 2022.

That assistance has helped Kyiv's forces regain ground from Moscow, and Ukrainian troops are currently engaged in a counteroffensive that has run up against heavy Russian defences.

Pope Francis, who became head of the worldwide Catholic Church in 2013, calls regularly for peace in Ukraine and his peace envoy visited Moscow in June, just weeks after visiting Kyiv.

Milley, a practising Catholic, said he and the Argentine pontiff discussed other issues as well, including talking "a lot about Africa".

The 86-year-old pope's "depth of knowledge of world events is quite impressive", said Milley.

"Just being there, having an opportunity to chat with him about issues of the day... was a real privilege."