Ukraine's military says its troops have been holding off the Russian forces' third offensive in Avdiivka, a strategically important city in the eastern region of Donetsk.

Ukrainian military commander Oleksandr Tarnavskyi revealed Russia had launched the attacks in a social media post on Thursday.

The General Staff of the Armed Forces of Ukraine said Russian forces were trying to surround Avdiivka, but Ukrainian troops staved them off. They also said the Russian side has suffered massive losses.

Russian forces have deployed large number of soldiers and armored vehicles to assault Avdiivka since last month, trying to take control of the entire Donetsk region.

The fighting is expected to intensify with the third wave.

Meanwhile, Russia's state-run TASS news agency reported on Thursday that a commander of a landing craft of Russia's Black Sea Fleet was killed in a Ukrainian drone attack. Ukrainian forces had said they conducted a military operation in Crimea in southern Ukraine on November 10. The commander is believed to have died in that strike.

Ukraine has been continuing its counteroffensive in Crimea, which Moscow unilaterally annexed in 2014.