The Russian military said Friday it had delivered its most advanced air defence system to Crimea after pledging last month to deploy it to the disputed region.

Russia's southern military district said in a statement carried by state news agencies that troops in Crimea had "received the modern S-400 'Triumph' air defence system".

The announcement comes as tensions between Ukraine and Russia have soared over the contested peninsula.

Russia's FSB security service said on Wednesday it had thwarted "terrorist attacks" in Crimea over the weekend by Ukrainian military intelligence and beaten back armed assaults, claims Kiev has fiercely denied.

The S-400 "Triumph" is Russia's latest anti-aircraft and missile defence system.

It has also been deployed to Syria, where Moscow is conducting a bombing campaign in support of long-time ally Syrian President Bashar al-Assad.

The system can track some 300 targets and shoot down around three dozen simultaneously over a range of several hundred kilometres.

Since Crimea's annexation Russia has stepped up its military presence in the peninsula, which is home to its Black Sea fleet.

The deployment of the S-400 to Crimea comes as NATO is rolling out the biggest military build-up in eastern Europe since the end of the Cold War and the United States has angered Moscow by installing a missile defence shield close to its borders.