Russian forces have intensified their offensive to take Ukraine's military stronghold in the country's east, exactly 20 months to the day since Russia launched its invasion of Ukraine.

Russia's military is reportedly deploying additional troops and ramping up its offensive around Avdiivka in the eastern region of Donetsk.

Ukrainian President Volodymyr Zelenskyy said in a video released on Monday that he is "especially grateful to the warriors" on the front in Avdiivka. He said, "Resilience there is a strength for all of Ukraine" and expressed his resolution to defend the embattled city.

Russia's defense ministry said on Tuesday that Russian naval forces had destroyed three unmanned boats after they were detected off the coast of Crimea.

The ministry also said an anti-mining and anti-sabotage operation was being carried out off the port city of Sevastopol, home of Russia's Black Sea Fleet.

Ukrainian forces have been conducting attacks on the Russian fleet in Crimea.

A spokesperson for Ukraine's defense ministry intelligence told local media on Saturday that Russia is feeling threatened and stressed that Ukraine is achieving results.

The spokesperson said the mission of the Ukrainian forces is to free Crimea and that they will need to destroy the occupiers for that purpose, indicating that they will continue to attack such targets as vessels armed with cruise missiles.