Monks have been secluding themselves from the world for more than a millennium in the caves of the Kiev-Pechersk Lavra, where 120 mummified brothers lie in glass-covered coffins along the low, sloping corridors.

Their solitude has been increasingly interrupted, however, since the top patriarch in Istanbul said in October he'd recognise a new Ukrainian church independent of Russia, sparking the biggest schism in Orthodox Christianity in 350 years.

On December 15, Ukrainian religious leaders will hold a “unification assembly” to lay the groundwork for the new church and choose its leader.

But the current Ukrainian Orthodox Church has remained loyal to the Moscow patriarchate even after Russia annexed Crimea in 2014 and backed separatists in an ongoing conflict in eastern Ukraine. It controls the Kiev-Pechersk monastery complex, a Unesco world heritage site and the holiest place in Ukraine, as well as 12,000 of the country's 18,000 churches.

Late last month, employees of the culture ministry, which technically owns the Kiev-Pechersk Lavra, suddenly came to take an inventory of the holy relics there. The next day, agents of the Ukrainian security service raided the Lavra as well as a residence belonging to the head abbot, charging him with the “incitement of religious hatred”.