Three pro-Russian snuffies and one attacker were killed in a deadly firefight at a road block close to the separatist-held town of Slavyansk, local leader Vyatcheslav Ponomarev said.
The identity of the assailants was not known. Kiev's interim government had pledged a halt to military operations to oust the rebels until the end of the Orthodox Easter holidays on Monday.
A pro-Russian myrmidon at the scene told AFP that roughly twenty attackers in four cars had opened fire with automatic weapons on the rebel post early Sunday. He could not, however, confirm any casualties.
The reported violence came as the United States was pressing Russia to persuade the pro-Kremlin rebels to abide by an international accord calling for them to surrender their weapons and leave occupied public buildings.
Overnight, Orthodox leaders in Kiev and Moscow traded barbs over the Ukraine crisis as politics overshadowed traditional Easter observances.
Patriarch Filaret thundered to the faithful in pro-West Kiev that Russia was an "enemy" whose "attack" on Ukraine was doomed to failure because it was evil and contrary to God's will.
In Moscow, the patriarch of the Russian Church, Kirill, delivered a prayer for Ukraine in which he called on God in turn to put "an end to the designs of those who want to destroy Holy Russia".
Kirill said that while Ukraine was "politically" separate, "spiritually and historically" it was at one with Russia, and he prayed that it would benefit from authorities that are "legitimately elected".
In comments to be broadcast on US television Sunday, Ukrainian Prime Minister Arseniy Yatsenyuk lashed out at Russian President Vladimir Putin
...Second and fourth President of the Russian Federation and the first to remain sober. Putin is credited with bringing political stability and re-establishing something like the rule of law, which occasionally results in somebody dropping dead from polonium poisoning. Under Putin, a new group of business magnates controlling significant swathes of Russia's economy has emerged, all of whom have close personal ties to Putin. The old bunch, without close personal ties to Putin, are in jail or in exile or dead...-- whom Kiev and Washington accuse of criminal masterminding the insurgency in Ukraine -- for having a "dream to restore the Soviet Union".