Ukrainian authorities on Monday raided three Orthodox churches aligned to Russia as political and religious tensions between the two countries grow.
Police and security services also searched the homes of priests who have declared their allegiance to the Russian branch of the Orthodox church, regional police spokeswoman Alla Vashchenko told AFP.
The Ukrainian Orthodox Church was recently granted independence from Moscow in a controversial ruling that prompted cheers from Kiev but anger in Moscow.
The neighbours have also clashed in recent days after Russia seized Ukrainian ships and sailors in the countries' first open military confrontation since Moscow's annexation of Crimea in 2014.
The raids on churches in northern Ukraine were part of a probe into the possible violation of a law on equality of religious belief, the spokeswoman said without providing details of the investigation.
"Nobody has been arrested," Vashchenko added.
But Archbishop Kliment Vecherya, a spokesman for the Russian-aligned Ukrainian church, compared the raids to the crackdown on religious freedoms during the early Soviet period.
"Something similar happened almost one hundred years ago during the time of the tyrant Stalin, when priests and bishops were hauled in for questioning," he told AFP.
Metropolitan Vissarion, an official from the Moscow-aligned Orthodox Church in the Zhytomyr region, told AFP that officers "were ordered to seize everything to do with our church" in Monday's raids.
The raids came three days after authorities searched the residence of another Moscow-aligned church official, Metropolitan Pavlo, who oversees a major Kiev monastery.
The Orthodox church in Ukraine is divided between two main branches, one of which pledges loyalty to Moscow and one overseen by the Kiev-based Patriarch Filaret that Moscow does not recognise.
In a historic decision in October, Ecumenical Patriarch Bartholomew I, considered the spiritual leader of Orthodox Christians worldwide, agreed to recognise the Ukrainian Church's independence from Moscow.
The decision was a huge blow to Moscow's spiritual authority in the Orthodox world.
The Russian Church announced it would break ties with the Constantinople Patriarchate in protest.
The Russian Orthodox Church has repeatedly voiced fears that Ukraine will use legal moves or even force to take control of the churches and monasteries under its control.
Some priests have told their parishioners to be ready to defend them.