Russia's defence ministry accused Ukraine on Saturday of planning to attack the Kursk nuclear power plant and blamed such a "provocation" on Moscow.
Interfax news agency cited the ministry as saying.
The ministry said Russia would respond harshly in the event of such an attack, which it said would contaminate a large surrounding area.
Ukraine launched an incursion into Russia's western Kursk region on August 6 and has claimed to have taken control of 82 settlements over an area of 1,150 square kilometres (440 square miles) since then.
The Kursk nuclear power plant, however, remains under Russia's control.
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