Putin on Wednesday announced an updated nuclear doctrine that would allow the use of nuclear weapons against non-nuclear states when they are supported by nuclear powers -- a clear reference to Ukraine and its Western backers.

"Not for the first time, Putin is playing (a) gamble with his nuclear arsenal," EU foreign policy spokesman Peter Stano told reporters. "We of course strongly reject these threats."

The proposed broadening of Russia's nuclear rules, which Putin himself has the power to approve, comes as Ukraine seeks permission from Western allies to use long-range weaponry to strike targets deep inside Russia.

Kyiv says it is necessary to target Russia's airfields and military infrastructure that it uses to launch attacks on Ukraine. The United States and other western countries are cautious about enabling further escalation.

Earlier on Thursday, Kremlin spokesman Dmitry Peskov said the planned changes should be seen as a "specific signal" to the West.

Western powers have accused Putin of dangerous nuclear sabre-rattling throughout the Ukraine conflict. The Kremlin leader has issued multiple apparent threats about Moscow's willingness to deploy nuclear weapons.

"This is just the continuation of the very irresponsible and unacceptable behaviour on the side of Putin," the EU's Stano said of the latest threat, which came as many world leaders attended the United Nations General Assembly in New York.

Putin's stance was all the more "reckless," Stano said, coming from the leader of a permanent member of the UN Security Council.