Pope Francis for the first time directly begged Russian President Vladimir Putin to stop the “spiral of violence and death” in Ukraine, saying on Sunday that the crisis was risking a nuclear escalation with uncontrollable global consequences.

In an address dedicated to Ukraine and made to thousands of people in St. Peter’s Square, Francis also condemned Putin’s latest annexation of parts of Ukraine as being against international law. He urged Putin to think of his own people in the event of an escalation.

One Vatican official said the impassioned address was so sombre it was reminiscent of a radio peace appeal by Pope John XXIII in 1962 during the Cuban Missile Crisis.

Saying he was haunted by “rivers of blood and tears that have been spilled in these months”, Francis also called on Ukrainian President Volodymyr Zelensky to be open to any “serious peace proposal”.

He was making an urgent appeal “in the name of God” for an end to the conflict and said it was “absurd” that the world was risking a nuclear conflict.

“My appeal goes above all to the President of the Russian Federation, begging him to stop this spiral of violence and death, even out of love for his own people,” Francis said.

“On the other side, pained by the enormous suffering of the Ukrainian population following the aggression it suffered, I address an equally hopeful appeal to the President of Ukraine to be open to a serious peace proposal,” he said.