Ukraine's nuclear power operator said on Tuesday that Russian forces were carrying out secret work at Europe's largest nuclear power plant, activity that could shed light on Russian claims that the Ukrainian military is preparing a "provocation" involving a radioactive device.
Russian Defense Minister Sergei Shoigu made an unsubstantiated claim that Ukraine was preparing to launch a so-called radioactive bomb. Shoigu made the accusation over the weekend in phone calls with his British, French, Turkish and American counterparts. Britain, France and the United States rejected the claim as "totally false".
Ukraine described Moscow's assertions as an attempt to divert attention from the Kremlin's alleged plans to drop a bomb, which uses explosives to disperse radioactive waste in an attempt to sow terror.
Energoatom, the Ukrainian state-owned company that operates the country's four nuclear power plants, said Russian forces have carried out secret work over the past week at the Zaporizhia nuclear power plant in Ukraine.
Russian officers controlling the site have refused to give access to Ukrainian personnel who run the plant or to monitors from the UN atomic energy watchdog to see what is going on there, the Energoatom company said in a statement released on Tuesday.
Energoatom said it "suspects" that the Russians are "preparing a terrorist act using nuclear material and radioactive waste stored" at the plant. He said that there were radioactive substances in 174 containers.
"Destruction of these containers as a result of an explosion will lead to an accident and radioactive contamination that could spread over several hundred square kilometers," the company said.
She called on the International Atomic Energy Agency to assess what is happening at the plant.
The Kremlin has insisted that its warning about a Ukrainian plan to use a nuclear bomb should be taken seriously and criticized Western countries for ignoring the concern.
Rejecting Moscow's warning is "unacceptable because of the seriousness of the danger we have talked about," Kremlin spokesman Dmitry Peskov said.
Speaking during a conference with journalists, Mr. Peskov added: "We again emphasize the great danger posed by the plans drawn up by the Ukrainians."
On Monday, the White House reiterated that the Russian claims were false.
"It's just not true. We know that's not true," said John Kirby, spokesman for the National Security Council. "In the past, in some cases, the Russians have blamed others for things that they were planning to do."
Nuclear fission bombs do not have the destructive capabilities of a nuclear bomb, but can expose a large area of land to radioactive contamination.