The Russian Orthodox Church has threatened to retaliate against its Istanbul-based rival if it allows Ukraine to cut its spiritual ties with Moscow and thereby end Russian religious rule in the country.

Metropolitan Hilarion, head of the Russian Orthodox Church's External Relations Department, said on September 8 that if the patriarch of Kyiv was recognized, "we will have no choice but to sever relations with Constantinople."

Hilarion also accused Istanbul-based Patriarch Bartholomew of Constantinople of acting in a "despicable and treacherous way."

Bartholomew, known as the "first among equals" of Orthodox Christian leaders in the world, is expected to rule in the coming months on an appeal from Ukraine to break away from Moscow and create an independent church.

The Russian Orthodox Church is especially upset with a decision on September 7 by Bartholomew to send two envoys to Ukraine as a step toward declaring ecclesiastical independence for the church there.

The Istanbul-based Patriarchate said it will send two bishops to Ukraine "within the framework of the preparations for the granting of autocephaly to the Orthodox Church in Ukraine," strongly suggesting it had already decided to grant independence to the Orthodox Church in Ukraine.

"When one brazenly and cynically interferes in the affairs of a local Orthodox Church, one creates not only a hopeless situation, but threatens the global Orthodox world with a schism," Russian news agencies quoted Hilarion as saying.

Bartholomew's rival in Russia, Patriarch Kirill, has called the prospect of the Ukrainian church being separated from Moscow an "all-Orthodox catastrophe."

The Russian church claims authority over the church in Ukraine. But many Ukrainian parishes reject the Moscow Patriarchate and have formed a separate church that is pushing for recognition as a self-governing, or autocephalous, institution.

The Orthodox Church in Ukraine is therefore split between a branch whose clerics pledge loyalty to Moscow and one that is overseen by the unrecognized Kyiv-based Patriarch Filaret.

While Constantinople is the oldest Orthodox Church, Moscow is currently the most powerful, with the largest number of worshippers.

It is unclear what granting Ukraine the right to create an independent church will mean in practice.

But experts say it would be a blow to Russia's spiritual authority in the Orthodox world.

The row comes against the backdrop of a four-year conflict between Kyiv and Russian-backed rebels in eastern Ukraine that has made many Ukrainians turn away from the Moscow church.

With reporting by AFP and AP