Throughout its two-year offensive on Ukraine, Moscow has repeatedly talked-up its arsenal of nuclear weapons and its readiness to deploy them if it senses an existential threat.

The West has accused President Vladimir Putin of irresponsible nuclear sabre-rattling.

Russia's defence ministry said Tuesday the drills were taking place in its Southern Military District, which borders and includes parts of Ukraine that Moscow claims to have annexed. It did not specify exactly where.

The drills are designed to test "the readiness of personnel and equipment of non-strategic nuclear weapons combat units to respond and to unconditionally ensure the territorial integrity and sovereignty of the Russian state," the defence ministry said in a statement.

It added they were a "response to provocative statements and threats by certain Western officials."

Putin ordered the drills earlier this month after a series of Western statements on the Ukraine conflict drew scorn in Moscow.

Russian officials pointed to comments by French President Emmanuel Macron about NATO countries needing to not rule out deploying troops to Ukraine and British Foreign Minister David Cameron saying Kyiv had the right to fire Western missiles at Russian territory.

Russia's Southern Military District is the command centre for its offensive on Ukraine. It is headquartered in Rostov-on-Don, 60 kilometres (40 miles) from the border with Ukraine and also includes parts of the country Russia says it has annexed -- the Crimea, Donetsk, Kherson, Lugansk and Zaporizhzhia regions.

The defence ministry published footage showing trucks carrying missiles to a field where launch systems were prepared and troops at an airfield readying a bomber to carry a nuclear warhead.

It said this was the "first stage" of the drills, which involved practicing the loading of launch vehicles, driving to designated launch sites and loading planes with hypersonic Kinzhal missiles.

It did not indicate whether any test firings had taken place.

Tactical nuclear weapons, also known as non-strategic nuclear weapons, are designed for use on the battlefield and can be delivered via missiles.