Ukraine's state nuclear energy company, Enerhoatom, has accused Russia of "kidnapping" two senior staff at the Russian-occupied Zaporizhzhya nuclear plant in southern Ukraine.
The plant's head of information technology, Oleh Kostyukov, and Oleh Oshek, an assistant to the nuclear station's director, were seized on October 17, Enerhoatom wrote on the Telegram app on October 18.
"At present, nothing is known of their whereabouts or condition," Enerhoatom's statement said.
Enerhoatom called on International Atomic Energy Agency (IAEA) chief Rafael Grossi "to make every effort" to secure their release.
The UN's nuclear watchdog said in a statement that Grossi "expressed deep concern about the recent detentions" of two staff members at the power plant, saying their detention had been confirmed by the IAEA.
"This is another concerning development that I sincerely hope will be resolved swiftly," Grossi said in the statement.
Russia detained the chief of the power station, Ihor Murashov, for several days late last month before releasing him on October 3. Grossi had been in contact with the relevant authorities to contribute to his release, the IAEA said.
It also said the IAEA team on site at the plant had learned of the release of a deputy director of the plant, Valeriy Martynyuk, who was detained early last week, the statement said.
Russian troops captured the Zaporizhzhya plant, Europe's largest, at the beginning of March, in the early days of Russia's unprovoked invasion of Ukraine.
The IAEA said on October 17 that the plant had again lost the connection to its last remaining power line and had to run its cooling and other safety systems on electricity from the grid through a back-up system. The October 18 statement said the connection to the power line had been restored.
"The repeated outages show how precarious the nuclear safety and security situation continues to be at Europe's largest nuclear power plant during the current military conflict in Ukraine," said Grossi, who has been pushing for a safety and security protection zone around the facility.