Russian President Vladimir Putin has signed into law a new lower threshold for the use of nuclear weapons by the state.

Previous military doctrine provided for the use of weapons of mass destruction in the event of a nuclear first strike by another nation, or if an attack by conventional weapons represented an existential threat to the Motherland.

The new lower threshold states nuclear capabilities can be deployed in the event of "aggression against Russia and its allies by any non-nuclear state supported by a nuclear state" or a large scale aerial attack with non-nuclear weapons.

Mr Putin first proposed such changes in September, citing “new sources of military threats and risks for Russia and our allies.”

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The new decree states: "Nuclear deterrence is also carried out in relation to states that provide the territory, air and/or sea space and resources under their control for the preparation and implementation of aggression against the Russian Federation".

The document, which comes into force immediately, also includes provisions for an attack on Belarus.

It states that Russia "reserves the right to use nuclear weapons" in the event of aggression against itself or its neighbour state with the use of conventional weapons which creates a critical threat to their sovereignty and/or territorial integrity.

Though the move was signalled in advance, it comes after outgoing President Joe Biden approved the use of US-made long-range missiles to strike targets within Russia which Moscow branded a "significant new round of escalation”.

Kremlin spokesperson Dmitry Peskov said: "This is a signal to warn these countries of the consequences that would ensue if they take part in an attack on our country using any means, not necessarily just nuclear.”

The new doctrine states one of the conditions for the possible use of nuclear weapons "is the receipt of reliable information" about a large-scale launch of air and space attack weapons (strategic and tactical aircraft, cruise missiles, unmanned, hypersonic and other aircraft) and their crossing of the state border of the Russian Federation.

When the potential change was announced in September, many experts viewed the move as one for the 'day after' the end of the Ukraine war, as a warning against any attempt to take territory annexed by Russia back into Ukrainian hands, a theory backed up by the reference to "territorial integrity".

Mr Putin's new decree states one of the principal dangers to the state as "the creation of new or expansion of existing military coalitions, leading to the approximation of their military infrastructure to the borders of the Russian Federation", likely a reference to his longstanding opposition to Ukraine joining NATO.

Russia has the largest stockpile of nuclear warheads in the world, with 5,580 as of 2024, and close to 2,000 actually ready to be launched.

The doctrine was last updated in June 2020 and described six 'military dangers' for which nuclear deterrence was needed.

Those were: the build-up by a potential adversary in territories adjacent to the Russian Federation and its allies and in adjacent maritime areas of general-purpose force groups that include nuclear weapons delivery vehicles; the deployment by states that view the Russian Federation as a potential adversary of missile defense systems and means, medium- and shorter-range cruise and ballistic missiles, high-precision non-nuclear and hypersonic weapons, strike unmanned aerial vehicles, and directed energy weapons; the creation and deployment in space of anti-missile defense systems and strike systems; the presence in states of nuclear weapons and (or) other types of weapons of mass destruction that could be used against the Russian Federation and (or) its allies, as well as the means of delivery of these types of weapons; uncontrolled proliferation of nuclear weapons, their delivery systems, technologies and equipment for their manufacture; and the deployment of nuclear weapons and their delivery systems on the territories of non-nuclear states.

The previous doctrine stated that Russia would consider using nuclear weapons if it received 'reliable information' of a ballistic missile launch against it or its allies; the use of nuclear weapons or other weapons of mass destruction against Russia, enemy actions which incapacitated its own nuclear deterrence; and "aggression against the Russian Federation using conventional weapons, when the very existence of the state is at risk".

That decree has been declared invalid following Mr Putin's new decree.