Russia says it will make changes to the doctrine that sets out the circumstances in which it might use nuclear weapons. What might that mean?
The current doctrine was set out by President Vladimir Putin in June 2020 in a six-page decree. It states, in part: "The Russian Federation reserves the right to use nuclear weapons in response to the use of nuclear weapons and other types of weapons of mass destruction against it and (or) its allies, as well as in the event of aggression against the Russian Federation using conventional weapons, when the very existence of the state has been placed under threat."
As this risk is not defined explicitly, Putin was able to make thinly veiled threats to use Russia's nuclear arsenal to deter any direct Western response to his despatch of troops into Ukraine in February 2022.
Putin's arms control point man, Deputy Foreign Minister Sergei Ryabkov, said on Sunday that the planned changes were "connected with the escalation course of our Western adversaries" in connection with the Ukraine conflict. He did not refer to specific events. Public discussion about the nuclear doctrine has been taking place for more than a year and intensified this year after French President Emmanuel Macron floated the possibility - dismissed by NATO alliance partners - that Western troops might be sent to fight in Ukraine.
Ultra-hawkish foreign policy expert Sergei Karaganov has said Russia should lower its threshold for using nuclear weapons in order to "contain, frighten and sober up our opponents", and that countries providing direct military support to Ukraine could be targeted.
"Over 75 years of relative peace, people have forgotten the horrors of war and even stopped fearing nuclear weapons ... That fear needs to be revived," Karaganov wrote in June 2023.
He argued that Russia's enemies needed to know that Moscow was prepared, if necessary, to deliver a pre-emptive, limited nuclear strike. If Russia used a nuclear weapon in Europe, Karaganov said, only a "madman" in the White House would respond with a nuclear or conventional attack on Russia because it would inevitably trigger a Russian nuclear strike on the U.S.
In a televised discussion at the St Petersburg Economic Forum on June 7, Karaganov directly asked Putin if Russia should "hold a nuclear pistol to the temple" of the West over Ukraine. Putin said Russia had no need to use nuclear weapons to secure victory, but that the nuclear doctrine was a "living instrument" that could change.
Nikolai Sokov, a former Russian and Soviet arms control diplomat, said the aim would be to send a signal to the West: "Don't forget about nuclear weapons. Be very, very careful."
But Sokov, a senior fellow at the Vienna Center for Disarmament and Non-Proliferation, said Russia would not announce changes publicly of the kind proposed by Karaganov.
Overtly lowering Moscow's nuclear threshold could severely antagonise countries that have avoided aligning themselves with the West against Russia: China, India, Brazil and others in the global south.
Instead, Russia might announce it had changed its policy but that the new doctrine would be kept secret - sending a signal to the West while also keeping it guessing.
In June, the head of the Russian parliament's defence committee said Moscow might shorten the decision-making time for using nuclear weapons if it perceived that threats were growing.
The risk of a nuclear war with Russia has deterred the U.S. and its NATO allies from sending their armies to fight alongside Ukraine's. Yet they have stepped up military aid to Kyiv in ways that were previously unthinkable, including by supplying tanks, long-range missiles and F-16 fighter jets. Ukraine has now crossed a new threshold by seizing a slice of Russian territory, which Kyiv says makes a mockery of Putin's "red lines" and shows that the West should now go all-out to help it win the war.
Sokov said it would be wrong, however, to conclude that Russia's nuclear signalling was empty talk, adding that it had already helped to slow the acceleration of Western assistance.
Furthermore, Russia has already taken concrete steps by stationing tactical nuclear missiles in Belarus and holding exercises this year to practise launching such weapons.
"It's a big mistake to say 'Oh, they're just talking'," he said. "When you change the doctrine, everyone should pay attention."
