Ukrainian President Petro Poroshenko has announced the creation of an independent Ukrainian Orthodox Church, marking a historic split from Russia.
He said national security depended on "spiritual independence" from Russia.
He was speaking at a special council of orthodox priests in Kiev, where a new leader of the church was selected.
The Russian Orthodox Church cut ties with the spiritual authority of the world's Orthodoxy after it recognised the Ukrainian Church's independence.
Russia also fears that its churches in Ukraine could be seized.
Despite Russia banning priests from the branch of the Church loyal to Moscow from the event, two of its bishops were seen arriving for the council in Kiev.
What happened in Kiev?
The special council was held in the ancient St Sophia's Cathedral - one of Kiev's best known landmarks.
Ukrainian clerics of different Orthodox denominations elected 39-year-old Metropolitan Epifaniy as the leader of the new church.
Epifaniy is now expected to travel to Istanbul on 6 January to receive a special decree, a tomos, granting independence (autocephaly) to the new church from the Ecumenical Patriarchate of Constantinople.
"This day will go into history as a sacred day... the day of the final independence from Russia," President Poroshenko told a crowd of thousands outside the cathedral.
Ahead of the meeting, Patriarch Kirill, the head of the Russian Orthodox Church, called on religious and world leaders to protect believers and clergymen in Ukraine from what he called persecution.
What is the dispute all about?
The Ukrainian Orthodox Church has been under the Moscow Patriarchate for centuries.
But tensions within the church mounted after Ukraine became independent in 1991, with the collapse of the Soviet Union.
Before Sunday's council in Kiev, there were three Orthodox Church branches in Ukraine:
- The Ukrainian Orthodox Church (Kiev Patriarchate)
- The Ukrainian Orthodox Church (Moscow Patriarchate)
- The Ukrainian Autocephalous Orthodox Church
Now, priests from the Kiev Patriarchate and the Autocephalous Church become members of the new church - the Orthodox Church of Ukraine.
The drive for Ukrainian Orthodox independence intensified in 2014, when Russia annexed Crimea and Russia-backed separatists seized a big swathe of territory in eastern Ukraine.
The Moscow branch of the Ukrainian Church has denied being a tool of the Kremlin, and says it has tried to bring about peace in eastern Ukraine.
Earlier this year, the Ecumenical Patriarchate of Constantinople - seen as the first among equals in the world's Orthodoxy - overruled its decision dating back to 1686 to transfer its jurisdiction over Kievan Orthodox churches (known as the Kievan Metropolis) to Moscow.
Now Moscow fears losing many of its 12,000 parishes in Ukraine.
Constantinople holds sway over more than 300 million Orthodox Christians across the world.
The Russian Orthodox Church is by far the biggest.