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.
US says it struck Iranian drone command sites at the weekend
US proposes new plan to ease Israel-Lebanon tensions amid fighting
At least two dead at Hanwha Aerospace fire in South Korea, official says
Netanyahu orders deeper Israeli incursion into Lebanon
Ebola recoveries bring signs of hope in DRC as suspected cases emerge outside Africa
