Pope Francis went to the Russian embassy to the Vatican 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 Argentine 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.
The ambassador was quoted as saying that the Argentine pontiff "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 on 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.
Several hours after meeting the ambassador, the pope telephoned Archbishop Sviatoslav Shevchuk, leader of Ukraine's Eastern-rite Catholics who has vowed not to leave Kyiv and who has opened up his cathedral's basement as a bomb shelter.
Shevchuk's Rome office said in a statement that the pope told the archbishop "I will do everything I can" to help.
Francis made many appeals for peace in Ukraine before the invasion on Thursday, but has not spoken publicly since. He has proclaimed Ash Wednesday as a day of prayer and fasting for peace in Ukraine.