Russia's defense ministry says the country's air force has thwarted an attempt by Ukrainian forces to land on Crimea, which was unilaterally annexed by Moscow.

The ministry said on Wednesday that Russian forces detected a group of Ukrainian soldiers in the Black Sea heading to a cape on Crimea's western end, using a high-speed boat and three jet skis. It said the attempt to enter Crimea was prevented.

On Tuesday, the ministry said that Russian air defense systems had downed a Ukrainian Neptune anti-ship missile over the Black Sea, off the coast of Crimea.

Ukraine has not reacted to the Russian announcement. But Ukrainian forces have been stepping up their attacks on Russian military facilities on Crimea.

The General Staff of the Ukrainian Armed Forces announced on Wednesday that counteroffensives are continuing towards the city of Melitopol in the southern region of Zaporizhzhia and the city of Bakhmut in the eastern region of Donetsk.

Officials said Ukrainian forces had partial success in some areas and inflicted losses on the Russian side.

A US think tank, the Institute for the Study of War, said in its assessment on Tuesday that it appeared combat capabilities of Russian paratroopers had been weakened and they could no longer conduct all counterattacks.