President Vladimir Putin warned the West on Wednesday that Russia could use nuclear weapons if it was struck with conventional missiles, and that Moscow would consider any assault on it supported by a nuclear power to be a joint attack.

The decision to change Russia's official nuclear doctrine is the Kremlin's answer to deliberations in the United States and Britain about whether or not to give Ukraine permission to fire conventional Western missiles into Russia.

Putin, opening a meeting of Russia's Security Council, said that the changes were in response to a swiftly changing global landscape which had thrown up new threats and risks for Russia.

The 71-year-old Kremlin chief, the primary decision-maker on Russia's vast nuclear arsenal, said he wanted to underscore one key change in particular.

"It is proposed that aggression against Russia by any non-nuclear state, but with the participation or support of a nuclear state, be considered as their joint attack on the Russian Federation," Putin said.

"The conditions for Russia's transition to the use of nuclear weapons are also clearly fixed," Putin said, adding that Moscow would consider such a move if it detected the start of a massive launch of missiles, aircraft or drones against it.

Russia reserved the right to also use nuclear weapons if it or ally Belarus were the subject of aggression, including by conventional weapons, Putin said.

Putin said the clarifications were carefully calibrated and commensurate with the modern military threats facing Russia - confirmation that the nuclear doctrine was changing.

Russia's current published nuclear doctrine, set out in a 2020 decree by Putin, says Russia may use nuclear weapons in case of a nuclear attack by an enemy or a conventional attack that threatens the existence of the state.

The innovations outlined by Putin include a widening of the threats under which Russia would consider a nuclear strike, the inclusion of ally Belarus under the nuclear umbrella and the idea that a rival nuclear power supporting a conventional strike on Russia would also be considered to be attacking it.

The United States in 2022 was so concerned about the possible use of tactical nuclear weapons by Russia that it warned Putin over the consequences of using such weapons, according to Central Intelligence Agency Director Bill Burns.

Confrontation

The 2.5-year-old Ukraine war has triggered the gravest confrontation between Russia and the West since the 1962 Cuban Missile Crisis - considered to be the closest the two Cold War superpowers came to intentional nuclear war.

Ukrainian President Volodymyr Zelenskiy has been urging Kyiv's allies for months to let Ukraine fire Western missiles, including long-range US ATACMS and British Storm Shadows, deep into Russia to limit Moscow's ability to launch attacks.

With Ukraine losing key towns to gradually advancing Russian forces in the country's east, the war is entering what Russian officials say is the most dangerous phase to date.

Zelenskiy has urged the West to cross and disregard Russia's so-called "red lines", and some Western allies have urged the United States to do just that, though Putin's Russia, which controls just under one-fifth of Ukrainian territory, has warned that the West and Ukraine are risking a global war.

"Russia no longer has any instruments to intimidate the world apart from nuclear blackmail," Andriy Yermak, Zelenskiy's chief of staff, said in response to Putin's remarks. "These instruments will not work."

Putin, who casts the West as a decadent aggressor, and US President Joe Biden, who casts Russia as a corrupt autocracy and Putin as a killer, have both warned that a direct Russia-NATO confrontation could escalate into World War Three. Republican presidential candidate Donald Trump has also warned of the risk of nuclear war.

Russia is the world's largest nuclear power. Together, Russia and the U.S. control 88% of the world's nuclear warheads, opens new tab.

In his remarks to Russia's Security Council, a type of modern-day politburo of Putin's most powerful officials including influential hawks, Putin said that work on amendments on changing the doctrine had been going on for the past year.

"The nuclear triad remains the most important guarantee of ensuring the security of our state and citizens, an instrument for maintaining strategic parity and balance of power in the world," Putin said.

Russia, he said, would consider using nuclear weapons "upon receiving reliable information about the massive launch of aerospace attack vehicles and their crossing of our state border, meaning strategic or tactical aircraft, cruise missiles, drones, hypersonic and other aircraft."