Russia's FSB security service on Tuesday accused Ukrainian "saboteurs" of repeatedly blowing up electricity pylons running from a nuclear reactor complex in the southern Russian region of Kursk, disrupting the plant's operations.
In a statement, the FSB said saboteur groups had targeted six high-voltage power pylons connected to the Kursk Nuclear Power Plant on Aug. 4, 9 and 12, leading to a "breach" in the plant's functioning.
"In cooperation with the (National Guard), measures were taken to enhance the protection of nuclear power facilities," the FSB statement said.
Reuters was not able to immediately verify the report.
Ukraine's defence ministry did not immediately respond to a request for comment.
Kursk is about 90 km (55 miles) from the Ukrainian border and one of several Russian cities to have been hit by explosions at fuel depots and ammunition dumps since Russia invaded Ukraine nearly six months ago.
Ukraine has not directly claimed responsibility but has described the incidents as "karma".
Since the start of the war, fears have grown for the safety of nuclear infrastructure, with Europe's largest atomic power plant in a Russian-occupied area of southern Ukraine coming under frequent shelling attacks.
Both Moscow and Kyiv have accused each other of heightening the risk of a nuclear accident. UN Secretary-General Antonio Guterres has called for an end to all military activities near the Zaporizhzhia reactor complex.
Earlier on Tuesday, Moscow blamed Ukrainian sabotage for explosions at a military base in the annexed region of Crimea. Ukraine has not officially confirmed or denied responsibility for the blasts.