Ukraine fired the deputy chief engineer of the Russian-occupied Zaporizhzhya NPP on Thursday, accusing him of cooperation with Moscow’s troops and treason, the state nuclear power company Energoatom reported.

The announcement came a day after Russia said it had appointed engineer Yuriy Chernychuk to the post of director of a huge nuclear power plant in southeastern Ukraine.

The nuclear plant, Europe’s largest, has been occupied by Russian troops since March and has stopped generating electricity since September, but is still operated by Ukrainian personnel to ensure its safety.

In October, Moscow said it had placed the plant under the control of Russian nuclear authorities, a move Kyiv considers illegal.

The former director was kidnapped

Ukraine claims that the head of the plant, Ihor Murashov, was kidnapped by Russian troops on the way to the plant in October.

Murashov was later released after Russian state television aired a video in which he confessed to “communication with Ukrainian special services.”

The IAEA observer from the UN said that he was allowed to join the family in the territory controlled by Ukraine.

“Yurii Chernychuk has become the new director of Zaporizhzhia NPP and the first deputy general director of Zaporizhzhia NPP,” said Renat Karchaa, adviser to the CEO of Rosenergoatom, evaluating him as a “courageous” successor.

The new director was allegedly held hostage

The state-owned nuclear company Energoatom said in May that Russia had barred Chernichuk from leaving the city of Energodar, where the plant is located, holding him and other employees “hostage.”

Since then, the six-reactor plant has been repeatedly bombed, prompting condemnation from the IAEA, the UN nuclear agency, which has called for a safe zone around it, which Moscow has so far opposed.

Russia and Ukraine accuse each other of bombing a plant located on the Russian-controlled bank of the Dnieper opposite Ukrainian territory. Kyiv also accuses Moscow of hiding military equipment at the plant, which Russia denies.