Ukraine sacked a top engineer at the Russian-occupied Zaporizhzhia nuclear power plant on Thursday, accusing him of collaborating with Russian forces, and urged other Ukrainian staff at the plant to remain loyal to Kyiv.
The head of state nuclear energy firm Energoatom made the appeal a day after Russia said it had promoted Ukrainian engineer Yuriy Chernichuk to serve as director of the vast plant in southeastern Ukraine.
"Instead of taking all efforts to liberate the station as fast as possible, he decided to help the Russian occupiers legalise its criminal seizure and is now inciting other atomic workers to do this," Energoatom chief Petro Kotin said.
Chernichuk could not immediately be reached for comment.
Moscow said in October it was putting Europe's largest nuclear power plant under the control of Russian nuclear authorities. Kyiv says the move is illegal.
"The only worthy option is to hold on!" Kotin told nuclear workers in a statement on the Telegram messaging app. "Hold on and don't sell your soul to the devil - don't sign pathetic 'contracts' with criminal Rosatom and affiliated firms."
Russia captured the plant in March, shortly after its invasion of Ukraine. Ukrainian technicians have continued to operate the facility but Kyiv has accused Russia of putting the technicians under immense pressure.
On Monday, Ukraine said Moscow had banned Ukrainian technicians who have refused to sign contracts with Russia's atomic energy firm from entering the plant.
Chernichuk had served as the facility's deputy engineer as well as the acting head engineer, Energoatom said.
"As far as Chernichuk is concerned, he's already fired from Energoatom and sooner or later he will answer for everything before the law and people. He has decided his destiny, your destiny is in your hands," Kotin told the plant's workers.
He dismissed as a "cynical lie" assertions that thousands of Ukrainian energy workers had switched sides to work for Rosatom.
The Zaporizhzhia facility has been a cornerstone of Ukraine's energy network for years and contributed up to around 20% of national electricity generation before Russia's invasion.
The six-reactor plant has not been producing electricity since September.
Russia and Ukraine have accused each other of shelling the facility, risking a nuclear catastrophe in the country that was the site of the world's worst nuclear accident at the Chornobyl atomic power station in 1986.
The United Nations' nuclear energy watchdog wants a nuclear safety zone established at the site. (Reporting by Tom Balmforth and Felix Hoske; editing by Timothy Heritage)