The Constantinople-based body recently recognised the independence of the Ukrainian Church from Moscow.
Tens of thousands of far-right activists marched through the centre of Kiev, waving red and black flags, a symbol of the nationalist movement, and blue and yellow Ukrainian flags. "It's an issue of Ukrainian statehood".
Ilarion said that Constantinople's decision to back what the Russian Orthodox Church considers a schismatic church is "illegal and canonically worthless", and effectively drives it into a schism.
"We are hoping common sense will prevail and that the Constantinople Patriarchate will change its relations to existing church reality", Metropolitan Hilarion said. The Finnish Orthodox Church also voiced hope that Patriarch Kirill of Moscow and All Russia and Patriarch Bartholomew of Constantinople "will be able to settle the dispute during the talks and relations will normalize as soon as possible".
According to the decision, priests from the two churches can not serve and worshippers can not take communion together. Sometimes they ceremonially bless Russian military jets and space rockets.
Like Vladimir Putin to whom he is close, Russian Patriarch Kirill deeply mistrusts the West. It brings together bishops of seven Orthodox churches, comprising some 2 million Orthodox Christians in Germany.More news: China plans to replace streetlights with ‘artificial moon’ by 2020
Yet, unless Moscow intervenes militarily-most likely again in a "hybrid" fashion by seeking to organize conflicts among Ukrainians-it has few other levers in this situation.
An influential Moscow cleric had earlier warned that parishioners would not hand over churches to a new Orthodox institution willingly.
Presidential spokesman Dmitry Peskov said Tuesday that the Kremlin was watching developments "very carefully and with a great deal of worry".
Given the longer-term harm it is now clear that the 2014 intervention did to Putin's neo-imperial project, however, any attempt to impinge on Ukraine's religious freedom would be even more misguided - and risky, The Financial Times editorial concludes.
After the visit in Ukraine in September of two sent by the Patriarchate of Constantinople, the Russian orthodox Church had already made a decision to break some of its ties with Constantinople.
Constantinople's move "is a big blow for Russia", Marat Shterin, a religious studies expert at King's College London, told the BBC.
About 100 million of the world's 260 million Orthodox Christians live in Russian Federation, according to the Pew Center.
But traditionally Constantinople has been seen as "first among equals".