Ukrainian President Petro Poroshenko on Saturday condemned the influential Russian Orthodox Church, which counts millions of believers, as a threat to national security.
The influence of the Russian Orthodox Church is a "direct threat to the national security of Ukraine", Poroshenko said during ceremonies marking 1,030 years since conversion to Christianity, adding that "this obliges us to act".
The Orthodox Church in Ukraine is split between the largest branch whose clerics pledge loyalty to the head of the Russian church, Patriarch Kirill, and one that is overseen by Kiev-based Patriarch Filaret.
Poroshenko joined a procession of tens of thousands of believers organised by the Kiev church after the Moscow-based church held a similar procession on Friday.
"I believe it is absolutely necessary to cut off all the tentacles with which the aggressor country operates inside the body of our state," Poroshenko said of the Russian church.
He complained that it is "separated from the state only on paper" while in reality it "fully and unconditionally supports the Kremlin's revanchist imperial policy."
In Moscow on Saturday, President Vladimir Putin headed a procession of worshippers with Russian Orthodox Patriarch Kirill, underlining their close relations.
Kirill even drew attention to the fact that Putin shares a first name with Prince Vladimir, who brought Christianity to the pagan Slavic state of Kievan Rus in 988.
"I think there is no such thing as a coincidence, especially when we are talking about people whose actions truly change the world," the Patriarch told Putin.
He prayed for peace among those fighting in the conflict between Kiev's forces and Russian-backed separatists in eastern Ukraine.
The conflict has exacerbated tensions between the two churches, with Ukranian Patriarch Filaret once saying Putin was "possessed by Satan".
The Kiev-based church supported the bloody popular uprising in 2014 that ousted a Kremlin-backed government in Ukraine.
Kirill on Friday warned against attempts to drive a wedge between the two churches.
"Attempts to artificially tear the Ukrainian Orthodox Church away from the Moscow Patriarchate can lead to a catastrophe," he said.