Constantinople's decision last week to end more than 300 years of Moscow's control over Orthodox churches in Ukraine was met with the Russian Orthodox Church's decision to split from Constantinople.
Orthodox Church leaders from numerous countries on Tuesday called for unity and raised fears of further discord after the Moscow branch announced it would break ties with the Istanbul-based Ecumenical Patriarchate, in what has been described as one of the gravest crises in the church's history.
The rupture on Monday came after the Istanbul-based clerics agreed to launch the process of recognising the independence of the Ukrainian Church, a move Russia has long campaigned against.
Constantinople's decision last week ended more than 300 years of Moscow's control over Orthodox churches in Ukraine and affects millions of believers in Russia and Ukraine.
While the Patriarch of Moscow up to now has formally overseen Orthodox churches in Ukraine, the country has two other Orthodox authorities which have splintered off without being recognised by Constantinople - until last week.
The religious split comes amid deep political tensions, with Ukraine opposing Russia's 2014 annexation of its Crimea peninsula and fighting a Moscow-backed uprising in its east in which more than 10,000 people have been killed.
The Russian Orthodox Church's head, Patriarch Kirill, is seen as a close ally of President Vladimir Putin.
Presidential spokesman Dmitry Peskov said on Tuesday that the Kremlin was watching developments "very carefully and with a great deal of worry".
Ukrainian President Petro Poroshenko meanwhile said the Russian Orthodox Church was following the Kremlin down a path of self-imposed isolation.
"Just as Russia opposed itself to the entire world community with its aggressive imperial policy, now the Russian Church is on the path of self-isolation and conflict with the world Orthodoxy," he wrote on his Facebook page.
The Ukrainian president and lawmakers have backed independence for the country's divided Orthodox Church and see it as striking a blow against Moscow's influence in Ukraine.
While the conflict grew out of the turbulent relations between Ukraine and Russia, a complete breach between the churches in Moscow and Turkey could threaten the integrity of the Orthodox Church as a whole, which has some 250 million believers around the world.
'Further splits possible'
The various Orthodox churches are already divided on the issue.
Serbian Patriarch Irinej said in an interview with a local news site: "We don't think in terms of 'for' and 'against'."
"We are for the unity of the Church, harmony, responsibility for canonical order, and against everything that divides and leads to the risk of schism."
At the same time he said that the recognition by Constantinople of an independent church in Ukraine was "a move that leads to schism" and opens up the possibility of new splits within other Orthodox churches.
Stevo Vucinic, vice-president of the Montenegrin Orthodox Church metropolis' council, welcomed the decision by Constantinople as of "historical importance" and slammed what he called a "political dispute" led by Moscow and Belgrade.
The Bishops' Conference of the Finnish Orthodox Church said the decision by Moscow was "unilateral, sad and very unfortunate" and hoped the patriarchs would resolve the conflict in mutual negotiations.
However Metropolitan Rostislav of the Orthodox Church in the Czech Lands and Slovakia wrote to Patriarch Kirill condemning "any attempt to legalise Ukrainian schismatics".
The Georgian Patriarchate said it would summon its Holy Synod shortly to decide on its position.
'Two warring Orthodox worlds'
Even Kremlin-loyal Russian media stressed that Moscow's move could lead to dire consequences.
The Izvestia newspaper, which strongly supports the Kremlin line, wrote that Monday will enter Orthodox history as "one of its darkest days".
The split between the Constantinople and Moscow Churches - the highest-status and largest Orthodox Churches respectively - followed on from the two greatest upheavals in Christian Church history, it wrote.
The front-page article referenced the Protestant Reformation of 1517 and the schism between the Eastern and Western Christian Churches in 1054.
Now each of the branches of the Orthodox Church "will have to choose with whom to be - Constantinople or the Russian Orthodox Church," Izvestia wrote.
The RBK business newspaper warned of a "war between (Holy) Synods" on its front page, referring to the Churches' ruling bodies.
A Russian expert on religion, Roman Lunkin, told RBK that Moscow's move has created "two warring Orthodox worlds".
Russian media including government newspaper Rossiiskaya Gazeta wrote with regret that Russians will no longer be able to go to pray at Mount Athos in Greece, an important destination for pilgrims and tourists that is under the jurisdiction of Constantinople.
For more on this, TRT World was joined from London by Alex Kokcharov, a Principle Research Analyst at the global information group IHS Markit.