The UN nuclear watchdog has voiced its mounting concern about the staff at the Russian-occupied Zaporizhzhya nuclear power plant in Ukraine as reports of physical abuse and interrogations of workers there emerge, the agency said Friday, adding that it must send a mission to the plant.

The International Atomic Energy Agency has said for months that the circumstances at the Zaporizhzhya ­— where Ukrainian staff are operating the complex under the order of Russian troops and staff from Rosatom, Russia’s state nuclear corporation — pose safety risks.

In its Friday statement the IAEA again insisted it must visit the Zaporizhzhya plant, Europe’s largest nuclear power facility — a request that has thus far been thwarted by both the Ukrainian and Russian sides.

“The IAEA is aware of recent reports in the media and elsewhere indicating a deteriorating situation for Ukrainian staff at the country’s largest nuclear power plant,” the statement by Rafael Grossi, head of the Vienna-based United Nations agency, said.

He further called the situation “untenable,” adding that: “We are informed that Ukrainian staff are operating the facility under extremely stressful conditions while the site is under the control of Russian armed forces. The recent reports are very troubling and further deepen my concern about the well-being of personnel there.”

The Zaporizhzhya plant and its six Soviet-built reactors was overrun by Russian troops in March 4 after a dramatic fire fight. A training facility adjacent to one of its reactors was shelled, raising fears that the siege could provoke a major nuclear accident.

In recent days numerous reports have emerged detailing the abuse the Zaporizhzhya plant’s Ukrainian nuclear workers are facing at the hand of occupying Russian troops. Many have documented brutal interrogations, torture and kidnappings as Russian soldiers attempt to ferret out those who sympathize with the Ukrainian side.

Some 500 Russian soldiers patrol the plant, these sources told the Wall Street Journal, reprimanding workers who speak in Ukrainian rather than Russian and screening their cellphones for evidence of allegiance to Kyiv. Those suspected of partisan leanings are rounded up — some never to return.

“People are being abducted en masse,” Dmytro Orlov, the exiled mayor of Enerhodar, the southeaster Ukrainian city where the Zaporizhzhya plant is located, said last week.

“The whereabouts of some of them are unknown. The rest are in very difficult conditions: They are being tortured and physically and morally abused.”

In its plea to visit the plant, the IAEA says it must be allowed to conduct physical inventories of the large amounts of nuclear materials — including some 30,000 kilograms of enriched uranium and 40,000 kilograms of plutonium said to be onsite.

Although remote transmission of data on that material to IAEA headquarters was restored this month, physical inventory verifications must still be carried out in person by inspectors within an interval that “cannot exceed a specified duration”, the agency said, without elaborating.

Two of the plant’s six reactors have recently been refuelled and such checks on that fuel are a prerequisite before restarting them, it added. Two reactors are currently operating.

Moscow has been ambiguous about its plans for the Zaporizhzhya plant. Alexey Likhachev, head of Rosatom, told state media that his company does not plan to take operational control of the complex — despite the presence of Rosatom officials at the site.

But Russian Deputy Prime Minister Marat Khusnullin on a visit to Russian-occupied Ukraine said that Kyiv may soon be forced to pay Moscow for the electricity produced at the plant — which amounts to a fifth of all power production in the country.