The head of Ukraine’s Orthodox Church Patriarch Filaret accused Russia of “aggression” and “evil”.
Russian Church Patriarch Kirill asked God to end the designs of those who wanted to rip apart Russia and Ukraine.
Pro-Russian activists in the east continue to occupy government offices.
Meanwhile Russia media are reporting several deaths in a gun battle near the eastern town of Sloviansk.
Reports of fatalities in the region have appeared before but have not been independently confirmed.
A mediator from the Organization for Security and Co-operation in Europe (OSCE) is scheduled to hold talks with them on Sunday.
Ertogrul Apakan, who heads the special OSCE mission in Kiev, said his deputy would be in Donetsk to try to get them to comply with an agreement reached on Thursday to ease the crisis.
In his Easter message, Patriarch Filaret said: “Against our peace-loving nation, which voluntarily gave up nuclear weapons, there has been aggression, there has been injustice.
“A country which guaranteed the integrity and inviolability of our territory has committed aggression. God cannot be on the side of evil, so the enemy of the Ukrainian people is condemned to defeat.
“Lord, help us resurrect Ukraine.”
In Moscow, Patriarch Kirill appealed for peace, saying it “should reign in the hearts and minds of our brothers and sisters by blood and by faith”.
But he also said Ukraine was “spiritually and historically” at one with Russia, and he prayed for it to have authorities that were “legitimately elected”.
“We are a single people before God,” he said.
Ukraine’s acting President, Oleksandr Turchynov, said in his Easter message: “We are living in a fateful time when the Ukrainian people have decisively affirmed their striving for freedom and justice.”
In an interview to be aired in full later on Sunday on NBC’s Meet the Press, Ukraine’s interim PM Arseniy Yatsenyuk accuses Russian President Vladimir Putin of trying to “restore the Soviet Union”.
If Vladimir Putin succeeded, Arseniy Yatsenyuk says, it would be “the biggest disaster of this century”.
Ukraine has been in crisis since President Viktor Yanukovych was toppled in February.
Russia then annexed the Crimean peninsula – part of Ukraine but with a Russian-speaking majority – in a move that provoked international outrage.
The annexation followed a referendum in Crimea that backed a move to join the Russian Federation.
Pro-Russian activists then occupied buildings in several eastern Ukrainian cities, many calling on Moscow to support them.
Russia, Ukraine, the EU and US agreed during talks in Geneva on Thursday that illegal military groups in Ukraine must be dissolved, and that those occupying government premises must be disarmed and leave.
But the separatists’ spokesman in the city of Donetsk said that the Kiev government was “illegal”, and vowed they would not go until it stepped down.
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