Ukraine struck three Russian oil refineries and an oil terminal in the Baltic Sea port of Vysotsk, Ukraine's military and ‌security service said on Monday, as ​Kyiv intensifies its attack on Russian energy infrastructure.

Explosions were recorded near the Slavneft-YANOS ⁠oil refinery in Yaroslavl region, and smoke ​was seen rising from the premises, the Ukrainian military's ⁠General Staff said on Telegram.

The refinery, which has come under Ukrainian attacks before, is among the biggest in Russia, ‌with annual oil refining capacity of ​15 million tons, ‌the General Staff said.

The General Staff added that NOVATEK-Ust ‌Luga refinery was hit in the Leningrad region.

The General Staff also said that a light ⁠petroleum products transshipment terminal in ‌Russia-annexed Crimea ⁠was hit.

Separately, Ukraine's Security Service, or the SBU, said ⁠on Telegram ⁠that together with other units it has struck the oil loading ‌terminal in Vysotsk, as well as an oil refinery in Kaluga region with drones.

Russian authorities said ‌that ​Ukrainian drone attacks ‌damaged the ports of Vysotsk and Ust-Luga, a major oil exporting outlet, and caused ​a power blackout in the Crimean city of Sevastopol.