The pope also told Italy's Corriere Della Sera newspaper on Tuesday that Patriarch Kirill of the Russian Orthodox Church, who has given the war his full-throated backing, "cannot become Putin's altar boy".

Francis, who made an unprecedented visit to the Russian embassy when the war started, told the newspaper that about three weeks into the conflict he asked the Vatican's top diplomat to send a message to Putin.

He said the message was "that I was willing to go to Moscow. Certainly, it was necessary for the Kremlin leader to allow an opening. We have not yet received a response and we are still insisting".

He added: "I fear that Putin cannot, and does not, want to have this meeting at this time. But how can you not stop so much brutality?"

Before the interview, Francis, 85, had not specifically mentioned Russia or Putin publicly since the start of the conflict on February 24.

But he has left little doubt which side he has criticised, using terms such as unjustified aggression and invasion and lamenting atrocities against civilians.

Australian Associated Press