The Russian Orthodox church has said it will not attend a historic meeting of all of the world's Orthodox churches because other churches have walked out.
The meeting on the Greek island of Crete due to start on Sunday would be the first in more than a millennium.
The Ecumenical patriarch, however, seemed to open the door for further talks that could prevent the meeting from falling through.
Orthodox church leaders have not held such a meeting since the year 787, when the last of the seven councils recognized by both Orthodox and Catholics, was held. The "great schism" that divided the Roman Catholics and the Orthodox followed in 1054 amid disputes over the Vatican's power.
Hilarion, a bishop who heads the Moscow Patriarchate's department of external church relations, said in a televised statement that Russia would not take part if others are walking out, and suggested the meeting be postponed.
"We have made a decision that we will not be able to take part in the all-Orthodox Synod if other churches do not go," Hilarion said.
The announcement of the Russian Orthodox church, with an estimated 100 million flock, is a heavy blow to the plans by Istanbul-based Ecumenical patriarch Bartholomew I, who had hoped the gathering of leaders from 14 independent Orthodox churches later this month could promote unity among the world's 300 million Orthodox Christians. Bartholomew I ranks as "the first among equals" in the Orthodox world.
The Moscow Patriarchate last week proposed holding a preliminary meeting to discuss the controversial issues raised by the Bulgarian church and others.
Reverend Alexander Karloutsos, a member of the organizing committee of the Great and Holy Council, told the Associated Press on Monday that they are inviting Moscow and other churches to meet and discuss the differences on 17 June.
"There is no mandate to change or postpone and we are going to proceed. They asked for a pre-conciliar meeting on the 17th and we expect to them to be here," he said. "We are the church of love and embrace everyone."
Bulgaria's Orthodox church put the plans in jeopardy last week saying it would not attend, citing differences over the agenda.
Unlike the Roman Catholic church, the Orthodox churches are independent and have their own leadership.
Hilarion said the Russian church will reach out to Bartholomew I to suggest postponing the meeting until the differences are resolved and all the churches agree to come. Russia will have to give the Crete gathering a miss if Bartholomew does not agree to reschedule, the Russian church said in a statement at the end of an extraordinary meeting in Moscow.
"All churches should take part in the all-Orthodox Synod and only in this case the decisions of this assembly will be legitimate," Hilarion said.
The Holy and Great Council has been 55 years in the preparation. Since the "great schism" there have been about a dozen smaller Orthodox councils over the centuries to discuss theological or doctrinal issues, but there has never been a meeting on this scale.
The council aimed to take up the mission and role of the Orthodox church and its global flock, issues relating to the function of the churches and relations with other Christian faiths. Unity of the Orthodox churches is considered a key prerequisite to any reconciliation with the Vatican.