"We asked him to come to Ukraine, to talk to (Russian President Vladimir) Putin, to tell him 'Let them go'. He just said he would pray for us," Kateryna Prokopenko told reporters after the brief encounter.

Her husband, Denis Prokopenko, is one of the leaders of the Azov regiment, a former far-right battalion turned National Guard unit who are leading the defence of the Azovstal steelworks in the southern Ukrainian port city of Mariupol.

The Ukrainians at the plant are the last pocket of resistance against the Russians, who now control Mariupol after weeks of siege.

"We hope that this meeting will just give us the chance to save their lives. We are ready for the actions of the pope, from his delegation, our soldiers are ready to be evacuated to a third country," Prokopenko said.

The women said their meeting with Pope Francis lasted around five minutes and took place after his weekly general audience on St Peter's Square.

Also in attendance was Verzilov, an associate of the punk group Pussy Riot and also publisher of Mediazona, an independent online publication which writes about court cases and abuses of prisoners' rights, among other subjects.

Yulia Fedosiuk, another member of the group of Ukrainian soldiers' wives, said they told the pope that "700 of our soldiers are injured, they have gangrene, amputations".

"Many of them are dead, we couldn't bury them, we asked the pope to help them, to be a third party in this war and to let them go through the (humanitarian) corridor," she said.

"He told us that he prays for us and that he is doing everything" he can.

She added that at the steelworks, "conditions are terrible there, no food, no water, no medical conditions -- the last hospital was destroyed by Russian bombs -- many dead soldiers".

Kyiv said on Tuesday that more than 1,000 of its troops, many of them injured, remained in the sprawling Azovstal plant, many sheltering in the labyrinth of Soviet-era bunkers and tunnels underground.

At the weekend, Deputy Prime Minister Iryna Vereshchuk said all women, children and elderly people had been evacuated from Azovstal as part of a humanitarian mission coordinated by the United Nations and the Red Cross.