Stress on workers at an occupied nuclear plant elevates risks, experts say.

When work started in southern Ukraine in 1981 on what would become Europe’s largest nuclear plant, the country was part of the Soviet Union and political instability barely figured as a risk. Today, Ukraine is at war with Moscow, the plant is occupied by Russian forces and experts say they are concerned about its safety.

Three problems at the Zaporizhzhia Nuclear Power Plant, in the city of Enerhodar and close to territory held by Ukraine, have caused particular worries.

Ukrainian officials say that Russian troops have installed artillery at the plant as a defense against a possible counterattack by Ukrainian forces looking to recapture territory lost since Russia invaded the country in February. A fire broke out in March during a Russian assault on the plant, and Russia later seized control of it.

The exiled mayor of Enerhodar, Dmytro Orlov, has detailed a series of episodes in recent weeks in which he claimed that some of the plant’s 11,000 employees were coerced to work by Russian forces. Some have been detained and interrogated as Russia searches for possible saboteurs, he said. Earlier this month, Mr. Orlov said that a diver at the plant had died after being tortured by Russian soldiers.

Mr. Orlov’s statements could not be independently confirmed. But officials from Energoatom, the state company that oversees the complex, have offered similar accounts based on interviews with workers at the plant, and witnesses in other occupied parts of Ukraine have relayed similar reports of mass detentions of civilians.

The director general of the International Atomic Energy Agency, Rafael Mariano Grossi, last week “expressed deep concern about the extremely difficult situation for Ukrainian workers at the plant.”

On Monday, in a further sign of how the plant has become politicized, the Ukrainian authorities said that a Russian film crew shot a video at the plant that was intended to show how Russian forces had improved security there.

But the most immediate problem, experts say, is transparency. Nuclear power plants routinely transmit safety data to the I.A.E.A. in Vienna. Twice in recent weeks, Zaporizhzhia’s data has gone offline. The agency said in a statement last week that the data transmissions had been restored after a weeklong interruption.

The transmissions, and regular visits by agency personnel, are viewed as fundamental to the safety architecture of all nuclear power plants. But the agency said its experts had not been to the Zaporizhzhia plant since the war began. Ukraine’s three other operational nuclear plants remain in government hands. Russian forces briefly took control of the defunct facility at Chernobyl — which in 1986 was the site of the worst nuclear accident in history — but withdrew in March.

“There is reason to be worried” about Zaporizhzhia, said Ulrich Kühn, the head of the arms control and emerging technologies program at the Institute for Peace Research and Security Policy at the University of Hamburg.

He described the situation as “bleak,” particularly given the lack of consistent monitoring, and argued that political stability, a prerequisite for civilian nuclear safety, was now absent at Zaporizhzhia.

“A big risk is that the workers are under maximum psychological stress,” he said. “What if they make a mistake?”

Mr. Kühn said that the international community should continue to express concern about instability at the plant, but to avoid turning the issue into part of the standoff over the war, countries viewed as neutral on Ukraine, such as Pakistan, could play a greater role in speaking out.