"Units of the southern military district that ended tactical exercises at training grounds on the Crimean peninsula are returning by rail to their permanent bases," the defence ministry said in a statement carried by Russian news agencies.

State-run television showed columns of military hardware crossing a recently-constructed bridge connecting the peninsula to the Russian mainland.

Thursday's announcement is the latest reported drawdown of a Russian military force estimated by the West to be more than 100,000 troops, which Washington had said could be preparing to invade.

NATO, the United States and European leaders have denied, however, that there is any meaningful pullback of Russian troops and Ukraine's President Volodymyr Zelensky said Moscow's military personnel were actually rotating.

Russia took control of the Crimean peninsula in 2014 and threw its weight behind pro-Moscow separatists in fighting that broke out that year and has claimed more than 14,000 lives.