Pope Francis went to the Russian embassy to the Holy See on Friday to relay his concern over Russia's invasion of Ukraine to Moscow's ambassador, in an unprecedented departure from diplomatic protocol.

Vatican spokesman Matteo Bruni said the pope spent more than half an hour at the embassy.

"He went to express his concern over the war," Bruni said, declining to give details about the visit or the conversation.

Bruni would not comment on an Argentinian media report that the pope, 85, had offered the Vatican's mediation. The ambassador, Aleksandr Avdeyev, denied this, according to the Rome correspondent of Russian TASS new agency.

Avdeyev told the RIA Novosti news agency that the meeting lasted about 40 minutes and that the pope expressed "great concern" about the humanitarian situation in Ukraine.

'Protection of Children, the Sick and Suffering'

The ambassador was quoted as saying that the pope "called for the protection of children, the protection of the sick and suffering, and the protection of people."

When contacted for comment by Reuters, the Russian embassy said the ambassador was not available.

The visit by a pope to an embassy to talk to an ambassador in a time of conflict is unprecedented in living memory.

Foreign envoys are usually summoned by the Vatican's Secretary of State or meet with the pope in the Apostolic Palace.

In an interview with Reuters of Feb. 14, before the invasion, Ukraine's ambassador to the Vatican, Andriy Yurash, said Kyiv would be open to a Vatican mediation of the conflict.

In a statement on Thursday, Vatican Secretary of State Cardinal Pietro Parolin said the Holy See hoped that those who hold the destiny of the world in their hands would have a "glimmer of conscience."

World leaders have accused Russian President Vladimir Putin of a flagrant violation of international law by launching the biggest attack by one state against another in Europe since World War Two.

Calls for Day of Prayer on Ash Wednesday

Francis made many appeals for peace in Ukraine before the invasion on Thursday, but has not spoken publicly since. He has proclaimed next Wednesday, Ash Wednesday, as a day of prayer and fasting for peace in Ukraine.

The Vatican announced separately on Friday that Francis would not be able to preside at the Ash Wednesday services because of an acute flare up of pain in his knee. He also will have to skip a trip to Florence this Sunday.