The UN’s atomic watchdog said Tuesday that the Chernobyl nuclear power plant is no longer transmitting data, expressing concern for workers working under Russian security at the Ukrainian facility.

On February 24, Russia invaded Ukraine and took control of the decommissioned Chernobyl nuclear power station, which was the site of a 1986 tragedy that killed hundreds of people and sent radioactive contamination over Europe.

The agency claimed in a statement that IAEA chief Rafael Grossi “reported that remote data transmission from safeguards monitoring devices installed at the Chornobyl NPP had been lost.”

“The Agency is investigating the status of safeguards monitoring systems in other parts of Ukraine and will give additional information as soon as possible,” the statement stated.

The International Atomic Energy Agency (IAEA) uses the word “safeguards” to describe technical procedures it applies to nuclear material and operations with the goal of preventing the spread of nuclear weapons by detecting misuse of such material early.

More than 200 technical professionals and security personnel have been stuck at the site for the past 13 days since the Russian takeover.

According to the IAEA, which cited the Ukrainian nuclear regulator, the situation for the workers at the facility was “worsening.”

The decommissioned plant is located within an exclusion zone that also houses deactivated reactors and radioactive waste storage facilities.

More than 2,000 people are still employed at the plant, which requires regular supervision to avoid another nuclear accident.

The UN agency urged Russia to enable workers to alternate shifts, citing the importance of relaxation and regular shifts for the site’s safety.

“I’m profoundly concerned about the tough and stressful situation that employees at the Chornobyl nuclear power plant are in, as well as the possible hazards that this poses to nuclear safety,” Grossi added.

“I demand that the forces in effective command of the site expedite the safe rotation of people there.”

Grossi renewed his offer to come to the facility or elsewhere to secure “the commitment to the safety and security” of Ukraine’s power plants from all stakeholders, with remote data transmission cut off and the Ukrainian regulator only able to reach the plant via email.

Last week, Russia attacked and captured Europe’s largest atomic power station, Zaporizhzhia, prompting Kyiv to accuse Russia of “nuclear terror.”

Zaporizhzhia alone has six reactors that are more modern and safer than the Chernobyl reactor that melted down.

Two of them were still operational, according to the IAEA, with the plant’s workers working in shifts and radiation levels remaining stable.