- Putin on Tuesday signed major changes to Russia's nuclear doctrine.
- The Kremlin said the changes were directed at Ukraine's ability to use US-supplied weapons in strikes on Russia.
- Biden approved their use on Sunday.
President Vladimir Putin approved an update to Russia's nuclear doctrine, widening the scenarios in which it would consider a strike.
The move seemed a direct response to events in Ukraine, where the US recently allowed Kyiv to use American weapons for longer-range attacks on Russia.
The changes, first mooted in September, were approved on Tuesday.
They build on a series of nuclear threats Putin has issued since the beginning of the full-scale war in Ukraine, though none have come to pass.
Western powers consider the use of nukes a disaster scenario that could escalate a now-regional war into a global conflict.
In the new doctrine, Russia said that attacks from a non-nuclear state could be considered as serious as those from a nuclear-armed one, if the nuclear states are helping.
That matches the situation being considered by Ukraine, which is receiving weaponry and intelligence support from Western allies including the US and has long wished to strike Russia with their weapons.
"The move is widely seen as a response to US and UK deliberations as to whether to allow Ukraine to fire conventional Western missiles into Russia," wrote the nuclear security expert Sitara Noor for the Lowy Institute in response to the September proposal.
Asked about this on Tuesday, Dmitry Peskov, the Kremlin's spokesman, told reporters: "Yes, this is what is being discussed."
The new doctrine also expands the circumstances for the potential use of nuclear weapons.
Before, Russia said it would consider their use in the event of detecting incoming ballistic missiles, or an attack that would harm its own nuclear capabilities.
Today, the doctrine says it'll consider nukes if it detects massive launches of weapons likestrategic and tactical planes, cruise missiles, drones, hypersonic and other aerial vehicles passing the Russian border, the state news outlet TASS reported.
Addressing the West
Putin proposed the latest changes the night before President Volodymyr Zelenskyy met with President Joe Biden to discuss allowing Kyiv to use ATACMS to make deep strikes in Russia.
This was "no coincidence," Alexander Gabuev, Director of the Carnegie Russia Eurasia Center wrote a few days later.
"Now the Russian leadership is ramping up its rhetoric in an attempt to stop the West from allowing Ukraine to fire NATO missiles into internationally recognized Russian territory," he added.
But the calculus has changed since September. On Sunday, it emerged that President Joe Biden gave the go-ahead.
That move was itself part of a wider reshaping of the war in anticipation of President-elect Donald Trump's return to power, as Business Insider's Sinéad Baker reported.