The United States and its allies have accused Russia of flagrantly violating international law by ordering troops into separatist regions of eastern Ukraine and recognising the breakaway Donetsk and Luhansk regions as independent republics.
Francis, speaking in a sombre tone at the end of his weekly general audience, also urged politicians to make "a serious examination of conscience before God" about the effects of their actions.
He proclaimed Ash Wednesday, on March 2 this year, as an international day of fasting and prayer for peace. He condemned the "diabolic senselessness of violence" and asked the Madonna, "the queen of peace, to save the world from the madness of war".
"I have great pain in my heart because of the worsening of the situation in Ukraine," Francis said, adding that he was anguished and worried like many around the world because peace was threatened by partisan interests.
"I appeal to all sides to abstain from any action that could provoke more suffering to the populations, destabilising coexistence among nations and discrediting international law."
The United States, the European Union, Britain, Australia, Canada and Japan announced plans to target banks and elites while Germany halted a major gas pipeline project from Russia in one of the worst security crises in Europe in decades.
It was the second time Francis has called an international day of prayer for peace in Ukraine. The first was on January 26.
"Jesus taught us that we should respond to the diabolic senselessness of violence with the weapons of God, with prayer and fasting," Francis said on Wednesday.Â
