Russia and Ukraine on Tuesday accused each other of plotting to stage an attack on the Russian-held Zaporizhzhia nuclear power station, long the subject of mutual recriminations and suspicions.
Russian troops seized the station, Europe's largest nuclear facility with six reactors, in the days following the Kremlin's invasion of its neighbour in February 2022.
Each side has since regularly accused the other of shelling around the plant, situated in Ukraine's south, and risking a major nuclear mishap.
Renat Karchaa, an adviser to the head of Rosenergoatom, which operates Russia's nuclear network, said Ukraine planned to drop on the plant ammunition laced with nuclear waste transported from another of the country's five nuclear stations.
"Under cover of darkness overnight on 5th July, the Ukrainian military will try to attack the Zaporizhzhia station using long-range precision equipment and kamikaze attack drones," Russian news agencies quoted Karchaa as telling Russian television. He offered no evidence in support of his allegation.
A statement issued by the Ukrainian armed forces quoted "operational data" as saying that "explosive devices" had been placed on the roof of the station's third and fourth reactors on Tuesday. An attack was possible "in the near future".
"If detonated, they would not damage the reactors but would create an image of shelling from the Ukrainian side," the statement on Telegram said. It said the Ukrainian army stood "ready to act under any circumstances".
The military also provided no evidence for its assertions.
None of the reactors at the plant is producing electricity.
The U.N.'s nuclear watchdog, the International Atomic Energy Agency, has been trying for more than a year to clinch a deal to ensure the plant is demilitarised and reduce the risks of any possible nuclear accident.
IAEA Director General Rafael Grossi has visited the plant three times since the Russian takeover but failed to clinch any agreement to keep the facility safe from shelling or other incidents linked to the conflict.
Mykhailo Podolyak, an adviser to Ukrainian President Volodymyr Zelenskiy, told Ukrainian television that Grossi had proved ineffective in trying to uphold safety at the plant. "Any disaster at Zaporizhzhia could have been prevented if (Grossi had been) clear straight away," Podolyak said, accusing the IAEA of flipflopping in his approach to the problem. "That is, instead of this clowning around that this man is doing. And when there is a disaster, he will say they had nothing to do with it and warned about the dangers."