Russia flexed its military muscle and put on a massive show of force in Crimea over the weekend, amid heightened tensions with the US and NATO.

So large and spectacular was the operation, Moscow issued a denial that the exercise was a demonstration of force designed to intimidate its traditional adversaries and wary neighbours.

Assembled journalists watched 12,000 troops in action on the land, fighter jets engage in mock dog fights above and cruise missiles launched from submarines positioned off the coast.

Strike fighters jets hit ground and sea targets while amphibious craft stormed beach heads in a wave of amphibious assaults.

Crimea, where the exercise unfolded, was annexed in 2014 by Russia, leading to diplomatic friction between Washington and Moscow.

Many observers believed Moscow was keen to show it was not leaving Crimea any time soon, and that it has immense strike power to wield if necessary.

Russia's military jets and navy ships combine to light up the sky off the Crimean coast. Source: AFP

Crew on a Russian military helicopter pull the trigger during a huge training exercise over the weekend. Source: AFP

However Russian Defence Ministry press spokesman General Igor Konashenkov said it was "absolute nonsense" that the weekend's activity was provocation.

"I want to emphasise once again that this was a planned event," General Konashenkov told NBC .

"This is absolutely not a demonstration [of force]. This is a drill which only has one goal - maintaining and improving combat readiness of the Russian Armed Forces."