Russia has been hit by a wave of sabotage incidents since attacking Ukraine in February 2022, almost all of which security forces blame on people working for Kyiv.

Oleksandr Maistruk and Eduard Usatenko, born in 1978 and 1974, attempted to blow up "more than 30 pylons on high-voltage power lines to the Leningrad and Kalinin nuclear power plants", Saint Petersburg court service spokeswoman Daria Lebedeva said on Telegram.

"The defendants wanted to shut down the nuclear reactors," she added, accusing them of working on behalf of Ukraine's Foreign Intelligence Service and of carrying out the attack on the eve of Russia's Victory Day on May 9.

The two men managed to blow up one pylon and planted explosives under 11 others, causing more than $100,000 worth of damage before they were caught, she said.

The Leningrad Nuclear Power Plant is less than 70 kilometres (43 miles) west of Saint Petersburg, Russia's second-largest city. The Kalinin plant in the Tver region is around 250 kilometres (155 miles) north of Moscow.

The two men were each given 23 years in a high-security prison and handed a fine of 900,000 rubles ($9,500).

Both Russia and Ukraine have accused the other of threatening security at nuclear power plants since the conflict began, with Moscow occupying Europe's largest nuclear station in Ukraine's southern Zaporizhzhia region.

Last year, the head of the International Atomic Energy Agency urged both sides to refrain from attacking power plants, warning that they were never "legitimate targets".