Vatican City: Pope Francis on Sunday deplored Russia's annexation of Ukrainian territory and called on the Russian leader to stop the war and on Ukraine's president to be open to talks.

"I deeply deplore the grave situation that has arisen in recent days, with further actions contrary to the principles of international law. It increases the risk of nuclear escalation, giving rise to fears of uncontrollable and catastrophic consequences worldwide," he said during the Sunday Angelus prayer.

He implored Russian President Vladimir Putin "to stop this spiral of violence and death" and on Ukrainian President Volodymyr Zelensky "to be open to serious proposals for peace".

He also urged the international community "to do everything possible to bring an end to the war, without allowing themselves to be drawn into dangerous escalations", and to support any efforts to resolve the conflict through dialogue.

It is the first time that the Argentine pope has directly addressed the Russian leader in a speech since the start of Moscow's invasion on February 24.

Francis has been trying since the start of the invasion to open a path of dialogue with Moscow, while condemning a "cruel and senseless war".