Russia test-fired missiles over distances of thousands of miles on Tuesday to simulate a "massive" nuclear response to an enemy first strike.
"Given the growing geopolitical tensions and the emergence of new external threats and risks, it is important to have modern and constantly ready-to-use strategic forces," President Vladimir Putin said as he announced the exercise.
It took place at a critical moment in the Russia-Ukraine war, after weeks of Russian signals to the West that Moscow will respond if the United States and its allies allow Kyiv to fire longer-range missiles deep into Russia.
In televised comments, Defence Minister Andrei Belousov told Putin that the purpose of the drill was to practice delivering "a massive nuclear strike by strategic offensive forces in response to a nuclear strike by the enemy."
The exercise involved Russia's full nuclear "triad" of ground-, sea- and air-launched missiles.