International atomic monitors are for the first time traveling through Russian territory rather than Ukraine to reach Europe’s biggest nuclear-power plant, said three diplomats briefed on the matter — a blow to Kyiv’s desire to avoid international recognition of the Kremlin’s ownership claims.

Ukraine said on Sunday it condemned a "breach of territorial sovereignty" by employees of the U.N. nuclear watchdog who visited the Russia-held Zaporizhzhia nuclear power plant in Ukraine via Russian-occupied territory.

The UN's nuclear watchdog defended itself on Monday against criticism from the Ukrainian government following the recent rotation of agency experts at the Russian-occupied Zaporizhzhya Nuclear Power Plant.