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, stated 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 added.

“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 added 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.

The 2-1/2-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 Zelensky has been urging Kyiv’s allies for months to let Ukraine fire Western missiles, including long-range U.S. 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.

Zelensky 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, Zelensky’s chief of staff, stated in response to Putin’s remarks.

“These instruments will not work,” he added.

Putin, who casts the West as a decadent aggressor, and U.S. 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.

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 continued.

Russia, he added, 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”.

His comments came as President Vladimir Putin on Wednesday escalated his nuclear rhetoric, telling a group of senior officials that Russia would consider using nuclear weapons if it was attacked by any state with conventional weapons.

In a speech to the UN General Assembly on Wednesday, the Ukrainian leader stated he had received information that Russia was gathering intelligence on Ukrainian nuclear power plants in preparation for a potential strike.

“Any missile or drone strike, any critical incident in the energy system could lead to a nuclear disaster … a day like that must never come,” Zelensky said in an address in the general assembly hall.

“And Moscow needs to understand this, and this depends in part on your determination to put pressure on the aggressor.”

He added: “These are nuclear power plants, they must be safe.”

Zelensky also said that the war in Ukraine could threaten the region with instability and the potential for a nuclear catastrophe if Russia went forward with the attacks.

“If, God forbid, Russia causes a nuclear disaster at one of our nuclear power plants, the radiation will not respect state borders,” he said, comparing the consequences to the Chernobyl nuclear accident of 1986. “And unfortunately, various nations could feel that devastating effects.”

Zelensky last month accused Russian forces of starting a fire on the site of the giant Zaporizhzhia nuclear plant, with its six Soviet-built reactors, making it Europe’s largest.

Russia captured the nuclear plant soon after its invasion of Ukraine in February 2022, and the plant has come under repeated attacks that both sides have accused each other of carrying out.

The International Atomic Energy Agency (IAEA) has repeatedly voiced concerns over the safety of the Zaporizhzhia nuclear plant, calling for “maximum restraint from all sides”.

As Zelensky was speaking in New York, Putin addressed Russia’s powerful security council on Wednesday, making his strongest warning yet to the west against allowing Ukraine to launch deep strikes into Russian territory using long-range western missiles.

Putin stated Russia would consider using nuclear weapons if Moscow gets “reliable information about start of mass cross-border attack by air from strategic and tactical aviation, cruise missiles, drones and hypersonic weapons”.

The Russian leader added that proposals had been made to change Russia’s nuclear doctrine, and said he would like to underscore one of the proposed key changes.

“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 stressed, in a thinly veiled threat to the west as foreign leaders continue to mull whether to allow Ukraine to use their long-range weapons.

Putin frequently invoked Moscow’s nuclear arsenal, the world’s biggest, in the early days of its invasion of Ukraine, repeatedly pledging to use all means necessary to defend Russia. He later seemed to moderate his rhetoric, but officials close to the Russian president have recently warned NATO countries they risk provoking nuclear war if they were to give the green light for Ukraine to use long-range weapons.

Earlier this month, Putin said the west would be directly fighting with Russia if it gave such permission to Ukraine – and that Russia would be forced to make “appropriate decisions”, without spelling out what those measures could be.

Zelensky is expected to travel to Washington to present his “victory plan” to Joe Biden at the White House on Thursday. The plan is a roadmap for Ukraine to end the war on its own terms, and is understood to include significant requests from the US and its allies for additional arms and economic and political support for Ukraine in the long term.

The Ukrainian president is expected to meet with Kamala Harris, who is running neck and neck with Donald Trump in the US presidential election. The Republican nominee is not expected to meet with Zelensky during the trip, and has threatened to severely cut aid to Ukraine if elected. In campaign rallies this week, Trump reiterated that he would “get out of Ukraine” if elected president.

In his speech, Zelensky stated Ukraine’s peace plan must be supported by world leaders, and that alternative initiatives to hold talks with Putin would simply aid the Russian president. Zelensky in particular targeted a joint proposal by China and Brazil, who have proposed a six-point peace plan for the Ukraine war without Kyiv’s backing.

“If someone in the world seeks alternatives … it likely means they themselves want to do a part of what Putin is doing … the question arises: what is the true interest?” Zelensky continued, adding, “Everyone must understand. You will not boost your power at Ukraine’s expense.”

In his speech, Zelensky also criticised the UN security council, saying it was “impossible to truly and fairly resolve matters of war and peace, because too much depends in the security council on the veto power”.

Russia is one of five permanent members of the security council and it exercises a veto power over any decisions taken by the body.

Without revealing additional details about the plan, which has been kept largely secret, Zelensky indicated it would not be adopted directly through the UN.

“When the aggressor exercises veto power, the UN is powerless to stop the war,” Zelensky said, adding, “But the peace formula … there is no veto power in it. That’s why it’s the best opportunity for peace.”