KYIV, Ukraine — Russia accused Ukraine on Saturday of damaging a nuclear waste storage facility in a drone strike on the Kursk nuclear power plant while fighting raged on for the control of the key eastern city of Avdiivika, where Russians apparently suffered heavy losses.

The Russian Foreign Ministry said that three drones armed with explosives targeted the power plant on Thursday evening. 26, hitting both the station’s administration building and a warehouse storing nuclear waste.

The press service for the Kursk nuclear power plant confirmed the strike on Friday, but told journalists that there had been no significant damage or casualties and that operations were continuing as normal.

Russia’s Defence Ministry said that the country’s air defences shot down six Ukrainian drones in the early hours of Saturday, including four in the western Oryol region, and two more over the Tula region, south of Moscow.

Ukraine’s air force reported four Iskander cruise missiles over the country’s Dnipropetrovsk region Saturday night, three of which were destroyed.

The apparent lull in aerial attacks at the start of the weekend follows several weeks of intense fighting close to the key city of Avdiivka, which lies in the Donetsk region of eastern Ukraine.

Ukrainian Defense Minister Rustem Umerov told his U.S. counterpart Lloyd Austin on Saturday that Russia had lost approximately 4,000 troops in Avdiivka, according to Kyiv’s Ministry of Defense.

Ukrainian President Volodymyr Zelensky also said Friday that Russia had lost at least a brigade trying to capture the embattled city, whose location provides Ukrainian forces with artillery advantages over the city of Donetsk and could serve as a launch pad for them to liberate the rest of the region.

Weeks of bitter fighting in the region have been costly, mostly for the Russian attackers, analysts say.

The bid to overrun Avdiivka has backfired on the Kremlin’s forces, robbing it of troops and heavy equipment that “will likely undermine Russian offensive capabilities over the long term,” the Institute for the Study of War said.

Satellite images show the Russian military lost at least 109 military vehicles, mostly armored fighting vehicles and tanks, near Avdiivika between Oct. 10 and 20, the institute said.