The Russian Foreign Ministry said Thursday that the goal of a proposed safety zone around the besieged Zaporizhzhia nuclear power station in southern Ukraine was to “stop Ukraine shelling” the plant, while Kyiv said Moscow was amassing advanced weapons at the site.

Both Moscow and Kyiv have accused each other of attacking Europe’s largest nuclear power complex, risking a potentially catastrophic nuclear accident.

Kyiv meanwhile said that that the plant’s Moscow occupiers have begun to deny entry to Ukrainian employees who have refused to sign contracts with Russia’s atomic firm, which now claims to oversee the plant.

Previous to the war, some 11,000 Ukrainians worked at the plant. That staff has now dwindled less than a quarter of that, posing another set of concerns around the plant’s safe operation.

In early October, Russian President Vladimir Putin signed an decree declaring that the plant and all of its assets belonged to a Russia-owned enterprise called JSC Operating Organization of Zaporozhye NPP. The United Nations nuclear watchdog — the International Atomic Energy Agency — has refused to recognize the Russian operator, saying in a statement that the Zaporizhzhia plant is a Ukrainian facility.

Since Russia launched its invasion in February, the Zaporizhzhia facility has come under repeated artillery attacks, prompting the IAEA to appeal for a demilitarized safety zone surrounding the plant.

Russia, which has been hot and cold on the issue, finally seemed to be warming to the proposal, though both sides have failed to agree to the details of what the initiative would look like.

IAEA Director General Rafael Grossi said earlier this week that the agency hoped to have an agreement on a secure zone in place by the end of this year.

“My commitment is to reach a solution as soon as possible. I hope by the end of the year,” Rafael Grossi told Italian newspaper La Repubblica in an interview published on Friday.

Grossi did not rule out meeting Russian President Vladimir Putin as well as Ukranian President Volodymyr Zelensky.

“Our goal is to avoid a nuclear accident, not to create a military situation that would favour either one party or the other”, Grossi said.

The Zaporizhzhia nuclear plant provided a fifth of Ukraine’s electricity before Russia’s invasion, and has been forced to operate on back-up generators a number of times. It has six Soviet-designed VVER-1000 water-cooled and water-moderated reactors running on uranium 235.

The reactors are shut down but there is a risk that nuclear fuel could overheat if the power driving the cooling systems is cut. Shelling has repeatedly cut power lines.