Without waiting for Washington, the European Union and the U.K. announced a new raft of sanctions against Russia.

The Vatican has a long history of conflict mediation, with varying degrees of success. An effort by the pope to end the war in Ukraine would face long odds.

Ukrainian President Volodymyr Zelenskiy said on Wednesday he had spoken by telephone to NATO Secretary General Mark Rutte, and that they had discussed joint steps and the need to put pressure on Russia to secure "a just peace".