Pope Francis on Sunday called on all sides in Ukraine to overcome "incomprehension" and appealed to the international community to promote dialogue.
"I ask you again to pray for Ukraine, which is experiencing a delicate situation," Francis said in his weekly Angelus blessing from a window of the Vatican Apostolic Palace overlooking St Peter's Square.
"I hope that all sides in the country work on overcoming incomprehension and build the future of the nation together," Francis said.
Francis: Who Is Pope Francis? Book Reveals the Man
"I make a heartfelt appeal to the international community to support any initiative in favor of dialogue and harmony."
Ukraine said Sunday it would call up all military reservists after President Vladimir Putin's threat to invade Russia's neighbor drew a blunt response from US President Barack Obama.
The stark escalation in what threatens to become the worst crisis in relations since the Cold War came as pro-Russian forces seized control of key government buildings and airports in the strategic Crimean peninsula.