Russia's Deputy Foreign Minister Alexander Grushko told Sputnik that the principles and conditions for using nuclear weapons by Russia are laid out in its military doctrine. 

When commenting on whether the use of a nuclear tactical strike on Ukraine is possible, Grushko stated that  "we have a military doctrine, everything is written there. It does not give any other interpretation than what is there in black and white."

Read more: Peskov: Russia will not use nuclear weapons unless faces existential threat

A presidential order authorized the basis of Russia's state strategy in the sphere of nuclear deterrence in June 2020. This paper establishes the concepts of nuclear deterrence, as well as the criteria for Russia's use of nuclear weapons.

These conditions include, among other things, receiving reliable information about the launch of ballistic missiles targeting the territories of Russia or its allies, the enemy using nuclear weapons or other types of weapons of mass destruction on the territories of Russia or its allies, and aggression against Russia using conventional weapons when the state's very existence is threatened.