The defence ministry said the exercises were taking place in the central and southern military districts -- which includes several North Caucasus republics and annexed Crimea -- as well as four regions of southern and eastern Ukraine that Russia claims to have annexed despite not fully controlling.

The southern military district includes the Russian city of Rostov-on-Don, which is home to Moscow's headquarters for the military operation in Ukraine.

"The third stage of non-strategic nuclear forces exercises have begun," said the Russian defence ministry in a statement.

This stage of drills involves training on the Iskander-M missile systems and various aircraft, the Russian defence ministry said.

The military personnel taking part will train on receiving "special ammunition" and on equipping missile systems and aircraft.

President Vladimir Putin in early May ordered the staging of these exercises partly, according to the Kremlin, in response to perceived threats from Western nations, notably after French President Emmanuel Macron broached the possibility of sending French troops to Ukraine.

The first stage of drills began in May.

Since the beginning of hostilities in February 2022, Putin has on occasions evoked the possible use of nuclear weapons.

In the summer of 2023, Russia deployed tactical nuclear weapons to its ally Belarus, which also borders Ukraine.

Minsk in May also announced synchronised military drills alongside Moscow to verify its tactical nuclear weapons launchers.