REUTERS - The Russian Defence Ministry said on Monday a long-planned major military exercise involving annexed Crimea and Russia's Black Sea and Caspian fleets had got underway, and that 12,500 troops would take part.

The exercise -- called Caucasus 2016 -- follows a period of heightened tension between Russia and Ukraine after Moscow accused Kiev of sending saboteurs into the peninsula to carry out a series of bombings. Kiev has flatly denied that.

Russia conducted a series of nationwide spot combat readiness checks in the run-up to the exercise and practiced swiftly moving military hardware and troops to Crimea as part of a logistics exercise last month.

The Defence Ministry described Caucasus 2016, which it said would run until Sept. 10, as the last major military training exercise of the year.

It said the war games, which are being held across Russia's entire southern military district, would test commanders' ability to plan, prepare and conduct military action and to coordinate different types of troops.

An unspecified number of aircraft would take part, along with Russia's Black Sea and Caspian Fleets, armoured units and infantry and paratroopers, it said.