President Vladimir Putin on Tuesday signed a directive formally lowering the threshold for Russia’s use of nuclear weapons, a move widely seen as a response to the recent policy shift by US President Joe Biden on the missile supply to Ukraine.

Under the new policy, Russia’s military could potentially deploy nuclear weapons in response to conventional military threats it perceives as an existential danger to the state. The Kremlin framed this shift as necessary to safeguard Russia’s sovereignty and territorial integrity in the face of heightened military threats. 

The United States’ approval of Ukraine’s use of US-supplied long-range missiles to strike Russian territory is speculated to be the primary motivator. The missiles are expected to be used strategically by Ukraine to strike critical Russian military positions far behind the front lines. US officials, while cautious about the potential for escalation, have argued that this support is essential for Ukraine’s self-defense against Russia’s invasion. The US move also follows reports that North Korea has provided military assistance to Russia, further complicating the conflict dynamics.

Russia will now regard ‘any attack by a non-nuclear country supported by a nuclear power as a joint attack’ and ‘reserves the right to consider a nuclear response.’ the Russian state news agency TASS reported. Kremlin spokesperson Dmitry Peskov stated: “[A]ny potential adversary must understand the “inevitability of retribution” for actions taken against Russia and its allies.”

The evolving situation raises important questions about the role of international law in mitigating conflict. The principle of proportionality, which underpins much of international humanitarian law, could be undermined if nations reduce the threshold for nuclear weapons use. Russia’s directive highlights the potential erosion of the legal norms that govern military conduct and nuclear deterrence.