A Ukrainian security agency has reportedly conducted a drone strike on a gas company facility at a Baltic Sea port in Russia, while a Moscow-installed official in Ukraine's eastern region of Donetsk says a Ukrainian attack has caused civilian casualties.

The governor of Russia's northwestern region of Leningrad said on Sunday that a fire broke out at the facility of major Russian private-sector gas firm Novatek. A Russian media outlet reports that two drones pounded the facility.

A Ukrainian media outlet quoted sources as saying the country's Security Service conducted a "successful overnight drone attack" on a gas terminal in Leningrad. The sources added that the strike "disrupts the logistical chain of fuel essential to the Russian military."

Meanwhile, a pro-Russian leader in the Donetsk region, Denis Pushilin, said on Sunday that a Ukrainian attack in the city of Donetsk left 25 people dead and 20 others wounded.

Russia's Foreign Ministry said in a statement that Ukraine carried out the strike with weapons supplied by the West. The ministry called the assault an "act of terrorism" and urged all countries and international organizations to condemn it.

The Russian military, for its part, has unleashed a barrage of missile and drone attacks in Ukraine.

A US think tank, the Institute for the Study of War, said in its assessment on Saturday that "Russian forces will likely continue to adapt missile and drone strike packages in an effort to penetrate Ukrainian air defenses and place pressure on Ukrainian air defense deployments."