CHERNYTSYA, Ukraine — Ukraine is on the verge of opening the biggest schism in Christianity in centuries, as it breaks from the authority of a Moscow-based patriarch and this week expects to formally gain recognition for its own church, taking tens of millions of followers.

Intensifying a millennium-old religious struggle freighted with 21st-century geopolitical baggage, Ukraine’s security services have in recent weeks interrogated priests loyal to Moscow, searched church properties and enraged their Russian rivals.

“They just want to frighten us,” said the Rev. Vasily Nachev, one of more than a dozen priests loyal to the Moscow patriarch who were called in for questioning.

The new Ukrainian church is expected to be granted legitimacy on Jan. 6, the eve of the Orthodox Christmas, when its newly elected head, Metropolitan Epiphanius, travels to Istanbul to receive an official charter from the Constantinople patriarchate, a longtime rival power center to Moscow.