The Kremlin said on Wednesday that Russia was adjusting its nuclear doctrine because the United States and its Western allies were threatening Russia by escalating the war in Ukraine and riding roughshod over Moscow's legitimate security interests.

Russia, the world's biggest nuclear power, is making changes to its nuclear doctrine, which sets out the circumstances under which Moscow would use such weapons - due to the West's increasing support for Ukraine which Russia invaded in 2022.

Kremlin spokesman Dmitry Peskov, in Moscow's most detailed explanation to date, linked the move directly to the "threats" created by the West and blamed the United States for destroying the post-Cold War security architecture of Europe.

The West, Peskov said, had rejected dialogue with Russia and taken a line of attack against its security interests while stoking "the hot war in Ukraine."

"It is the United States that is the ringmaster of the process of provoking tension," Peskov said.

Peskov indicated that revision of the nuclear doctrine was at an early stage, saying that the current tensions would be analysed carefully and then form the basis of proposed changes.

Russia's current published nuclear doctrine, set out in a 2020 decree by President Vladimir 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.

Russia and the United States are by far the world's biggest nuclear powers, holding about 88% of the world's nuclear weapons, according to the Federation of American Scientists. Both are modernising their nuclear arsenals while China is rapidly boosting its nuclear arsenal.

The war in Ukraine has triggered the biggest confrontation between Russia and the West since the 1962 Cuban Missile Crisis, with both sides saying they cannot afford to lose the conflict.

UKRAINE WAR

As Russia, which now controls 18% of Ukraine, advances, Kyiv has repeatedly asked for more Western weapons and permission to use Western-supplied long-range weapons in its attacks far into the Russian territory.

The U.S. is close to an agreement to give Ukraine long-range cruise missiles that could reach deep into Russia, but Kyiv would need to wait several months as the U.S. works through technical issues ahead of any shipment, U.S. officials said.

Sending Joint Air-to-Surface Standoff Missiles (JASSM) to Ukraine could significantly alter the strategic landscape of the war by putting more of Russia in range of powerful, precision-guided munitions, an important concern of the Biden administration, the officials said.

Peskov said it was obvious that Ukraine would move to striking targets deep in Russia with Western weapons.

Russia's foreign ministry said if Russia was struck with long-range weapons, the response would be immediate and "extremely painful".

"They are losing their sense of reality, they absolutely do not think about the risks of further dangerous escalation of the conflict, even in the context of their own interests," Maria Zakharova, spokesperson for the foreign ministry, said.

"We would like to warn such irresponsible politicians in the EU, NATO, and overseas - in case of appropriate aggressive steps by the Kyiv regime, Russia's response will follow immediately."

(Reporting by Reuters; writing by Guy Faulconbridge; Editing by Ros Russell)