"Shoigu flew by helicopter around areas where troops and military equipment are deployed and inspected the readiness of sea and land groups taking part in the exercises," the defence ministry said in a statement.

The drills come against the backdrop of renewed tensions between Russia and Ukraine's Western allies, who have voiced concerns about a build-up of Russian troops on the border and drills in Crimea.

The defence ministry told the Interfax news agency that some 10,000 ground troops and more than 40 warships were participating in the Crimea exercises.

They come after Russian news agencies citing the defence ministry reported last week that Moscow intends to close parts of the Black Sea to foreign military and official ships for six months beginning Saturday.

The move could affect access to Ukrainian ports in the Sea of Azov, which is connected to the Black Sea through the Kerch Strait on Crimea's eastern tip.

The European Union called it a "highly worrying development," while NATO also expressed "concern" and called on Russia to guarantee "free access" to Ukrainian ports.

Russia in recent weeks has sent tens of thousands of troops to its borders with Ukraine and Crimea, deployments that Shoigu described as training exercises in response to "threatening" NATO actions.

Ukraine has been battling pro-Russian separatists in its east since 2014, in a conflict that erupted after Moscow annexed Crimea.