The Vatican confirmed on Monday that Pope Francis will travel next month to Kazakhstan, where he could meet with Patriarch Kirill, the leader of the Russian Orthodox Church, who has justified Moscow's war in Ukraine.

Francis, 85, will attend an interfaith conference in the Kazakh capital, Nur-Sultan, from September 13-15, the Vatican said.

Francis called off a planned encounter with Kirill in June in Jerusalem because of the diplomatic fallout it would have created.

Kirill has justified the invasion on spiritual and ideological grounds, calling it a “metaphysical” battle with the West. He has blessed soldiers going into battle and invoked the idea that Russians and Ukrainians are one people.

Francis and Kirill, who had a first historic encounter in Havana in 2016, have spoken by video call at least once since the war began.

The Kazakh government is hosting a “Congress of Leaders of World and Traditional Religions” from September 14-15. Kirill has been invited and the Moscow Patriarchate has said he would attend.

Returning from his just-concluded trip to Canada, Francis told journalists on Saturday that in addition to Kazakhstan, he also hoped to visit Ukraine but that nothing had yet been confirmed. Vatican officials have said they hoped to organize a trip even in the coming weeks.

On Sunday, Francis again prayed for Ukraine, saying he had never stopped praying for “the attacked, martyred Ukrainian people”, during his Canadian pilgrimage.

“If you look at reality objectively, considering the damage that war brings every day to those people but also the entire world, the only reasonable thing to do is to stop and negotiate,” he said. “May wisdom inspire concrete steps of peace."

Francis has criticised Russia's invasion of Ukraine and Kirill's support for the war, telling an Italian newspaper in May that the patriarch shouldn't become "Putin's altar boy”.

The Russian Patriarchate shot back that it was regrettable” that Francis “chose the wrong tone” to relay the contents of their March video call.