Ukrainian officials said Wednesday a massive Russian aerial attack that included 55 missiles and 21 drones damaged a power generation facility in the Lviv region of western Ukraine.

DTEK, Ukraine’s largest private electricity company, said Russian missiles inflicted “serious damage” on three of the company’s six thermal power plants in Ukraine.

Maksym Kozytskyi, the regional governor of Lviv, said on Telegram that Russian cruise missiles struck the generation facility in the Chervonohrad district as well as a critical energy infrastructure site in the Stryi district.

There were no reports of casualties.

Andriy Rakovych, the regional governor of central Ukraine’s Korovohrad region, reported one person injured and 13 homes destroyed in a Russian missile attack.

Officials in Vinnytsia also reported a Russian strike in attacks targeting critical infrastructure facilities.

Ukraine’s air force said the country’s air defenses shot down 39 of the 55 missiles and 20 of the 21 drones.

The attack came a day after Ukrainian counterintelligence investigators said they thwarted a plan by Russian agents to assassinate Ukrainian President Volodymyr Zelenskyy and other high-level officials.

Ukraine’s state security service said two colonels in the State Guard of Ukraine, which protects top officials, were arrested on suspicion of treason for enacting the plan. A state security service statement said the plot was drawn up by Russia’s Federal Security Service.

Russia did not immediately comment on the reports, which indicate that the colonels were recruited prior to Russia’s full-scale invasion of Ukraine in February 2022.

Some information for this report was provided by Reuters, The Associated Press and Agence France-Presse.