The Russian Orthodox Church says it is cutting all links with the Constantinople Patriarchate – the body that wields spiritual authority over the world’s Orthodox Christians.
Constantinople recently recognised the independence of the Ukrainian Church from the Moscow Patriarchate.
Many Ukrainian Christians accuse the Russian Church of favouring Russian-backed rebels in eastern Ukraine.
Constantinople holds sway over 300 million Orthodox Christians globally.
Moscow rejects the independence of the Ukrainian Church.
Metropolitan Hilarion, the bishop who heads the Russian Orthodox Church’s diplomacy, told reporters in Belarus: “A decision has been made to rupture full communion with the Constantinople Patriarchate.”
The bishop said Constantinople’s decision to recognise all Ukrainian churches as independent from Moscow went “against historical truth”.
Constantinople had previously rejected the Ukrainian Church’s independence moves, but decided to endorse them last week.
Ukrainian President Petro Poroshenko said the Church’s independence went hand-in-hand with Ukrainian independence.
“It’s an issue of Ukrainian national security. It’s an issue of Ukrainian statehood.”
Ukraine became independent of Russia in 1991, but Russia’s annexation of Crimea in 2014 and the fighting in eastern Ukraine have poisoned relations.
The Moscow Patriarchate has denied being a tool of the Kremlin and says it has tried to bring about peace in eastern Ukraine.
The Patriarchate says it hopes Constantinople will change its mind on recognising the independence of the Ukrainian Church so that a schism can be avoided.
Russia sees Kiev as the historic cradle of the Russian Orthodox Church.
The Kremlin has said recently that it fears clashes in Ukraine over Orthodox sites where services by the Moscow Patriarchate are held.