The Russian military said Tuesday it had launched exercises involving some 6,000 troops and at least 60 fighter jets in southern Russia near Ukraine and in Moscow-annexed Crimea.

The southern military district described the live-fire drills as a combat readiness check, as tensions rage between Moscow and the West over Crimea.

"Units will practice carrying out a wide range of tasks, including the organisation of comprehensive support for tactical exercises," the defence ministry said in a statement.

"Combat firing exercises will also be held using all types of aviation, missile divisions and ship groups of the Black Sea Fleet and the Caspian Flotilla."

Fighter jets and bombers will practise carrying out air strikes "against targets at the maximum distance", among other tasks, Russian news agencies said, quoting the defence ministry.

The drills will take place in Russian-annexed Crimea and the southern Rostov and Krasnodar regions.

There was no indication of how long the exercises would last.

The West is accusing Russia, which has massed 100,000 troops on the Ukrainian border, of preparing a potential invasion of its pro-Western neighbour.

The troop build-up has sparked the biggest crisis in East-West ties since the Cold War.