KYIV, Ukraine (AP) — Russian air defense shot down over 30 Ukrainian drones over the Black Sea and the Crimean peninsula overnight Saturday, Russia’s Defense Ministry said Sunday.

“The air defense systems in place destroyed 36 Ukrainian unmanned aerial vehicles over the Black Sea and the northwestern part of the Crimean peninsula,” the ministry wrote on Telegram.

Local authorities in the southern Krasnodar region bordering the Black Sea said that a fire broke out at an oil refinery in the early hours of Sunday, but did not specify the cause. “The reasons for the incident are being established,” a statement from local authorities said, amid claims in local media outlets that the fire had been caused by a drone strike or debris from a downed drone.

Drone strikes and shelling on the Russian border regions and Moscow-annexed Crimea are a regular occurrence. Ukrainian officials never acknowledge responsibility for attacks on Russian territory or the Crimean peninsula.

In Ukraine, the country’s air force said Sunday it had shot down five Iranian-made Shahed exploding drones launched by Russia overnight.

Close to the front line in the country’s east, where Ukrainian and Russian forces are locked in a grinding battle for control, four police officers were wounded when a shell fired by Russian troops exploded by their police car in the city of Siversk, located in the partly occupied Donetsk province.

British intelligence assessed this weekend that Russia had suffered some of its biggest casualty rates so far this year as a result of continued “heavy but inconclusive” fighting around the town of Avdiivka, also in the Donetsk province. The UK Ministry of Defence’s regular intelligence update on Saturday morning noted that Russia had committed “elements of up to eight brigades” in the area since it launched its “major offensive effort” in mid-October.

Also on Sunday, a prominent ally of Russian President Vladimir Putin warned that Russia might take action to seize assets of European Union member states it considers hostile if the EU proceeds with its plan to “steal” frozen Russian funds to support Ukraine’s post-war reconstruction efforts.

“A number of European politicians (...) have once again started talking about stealing our country’s frozen funds in order to continue the militarization of Kyiv,” Vyacheslav Volodin, the Chairman of the State Duma, the lower house of Russia’s parliament, wrote on Telegram.

Volodin made the statement in response to an announcement on Friday by Ursula von der Leyen, the president of the European Commission, on a proposal to use earnings from frozen Russian state assets to support Ukraine in its rebuilding.

Volodin asserted that Moscow would respond with measures that would inflict significant costs on the EU if it were to take action against Russian assets, a considerable portion of which are in Belgium.

“Such a decision would require a symmetrical response from the Russian Federation. In that case, far more assets belonging to unfriendly countries will be confiscated than our frozen funds in Europe,” Volodin said.