KIEV, Ukraine — Ukraine’s president announced Thursday that the Constantinople patriarchy has approved a decree granting the Ukrainian Orthodox Church independence from the Russian Orthodox Church, a major boost to the president’s approval ratings.

The Ukrainian church has formally been under the Russian Orthodox Church for centuries, so this step would be momentous, splitting the world’s largest Eastern Orthodox denomination. It would also severely erode the power and prestige of the Moscow Patriarchate, which has positioned itself as a leading player within the global Orthodox community.

Both the Russian Orthodox Church and Russian authorities are strongly against the move and have warned Ukraine not to do it.

Yet Ukrainian President Petro Poroshenko has made an independent church one of the key slogans of his not-yet-announced campaign to stay in office. The presidential election is scheduled for next March and Poroshenko in recent polls was seen lagging behind his archrival, former prime minister Yulia Tymoshenko.

The Istanbul-based patriarch Bartholomew, considered “first among equals” of all Orthodox church leaders, earlier this year took the first major step toward granting the Ukrainian church a “Tomos of Autocephaly,” or full ecclesiastic independence, when he removed condemnation of leaders of schismatic Orthodox churches in Ukraine.

“A historic decision has been made to set up an autocephalous Ukrainian Orthodox Church,” Poroshenko said Thursday. “The text of the Tomos to grant the Ukrainian church independence has been approved.”

Ukraine currently has three Orthodox communities — one that stays under Moscow’s control and two schismatic churches.

Recognition of a Ukrainian church that is not under Moscow’s jurisdiction has been an increasingly fraught issue amid the high tensions over Russia’s 2014 annexation of the Crimean Peninsula and its support of separatist rebels in eastern Ukraine.

Those tensions escalated this week when Russian authorities rammed and seized three Ukrainian vessels and 24 seamen near Crimea on Sunday.

Orthodox communities will now have to convene at a date announced by Bartholomew I to formally form a new church, Poroshenko said Thursday.

The Russian church has severed its links with Bartholomew I to protest granting independence to the Ukrainian church. Moscow fears that splitting the Orthodox community in Ukraine could trigger sectarian violence.