The existing nuclear doctrine, set out in a decree by President Vladimir Putin in 2020, says Russia may use nuclear weapons in the event of a nuclear attack by an enemy or a conventional attack that threatens the existence of the state.

Some hawks among Russia's military analysts have urged Putin to lower the threshold for nuclear use in order to "sober up" Russia's enemies in the West.

Putin said in June that the nuclear doctrine was a "living instrument" that could change, depending on world events. Ryabkov's comments on Sunday were the clearest statement yet that changes would indeed be made.

"The work is at an advanced stage, and there is a clear intent to make corrections," state news agency TASS cited Ryabkov as saying.

He said the decision is "connected with the escalation course of our Western adversaries" in connection with the Ukraine conflict.

Moscow accuses the West of using Ukraine as a proxy to wage war against it, with the aim of inflicting a "strategic defeat" on Russia and breaking it apart.

The United States and its allies deny that, saying they are helping Ukraine defend itself against a colonial-style war of aggression by Russia.

'RED LINES'

Putin said on day one of Russia's full-scale invasion of Ukraine in February 2022 that anyone who tried to hinder or threaten it would suffer "consequences that you have never faced in your history".

Since then, he has issued a series of further statements that the West regards as nuclear threats, and announced the deployment of Russian tactical nuclear weapons in Belarus.

That has not deterred the U.S. and its allies from stepping up military aid to Ukraine in ways that were unthinkable when the war started, including by supplying tanks, long-range missiles and F-16 fighter jets.

Ukraine shocked Moscow last month by piercing its western border in an incursion by thousands of troops that Russia is still fighting to repel.

President Volodymyr Zelenskiy said the operation made a mockery of Putin's "red lines". He is also lobbying hard for the U.S. to allow it to use advanced Western weapons to strike targets deep inside Russia.

Kremlin spokesman Dmitry Peskov said in an interview published on Sunday that the West was "going too far" and that Russia would do everything to protect its interests.

Ryabkov did not say when the updated nuclear doctrine would be ready. "The time for completing this work is a rather difficult question, given that we are talking about the most important aspects of ensuring our national security," he said.

Russia has more nuclear weapons than any other country. Putin said in March that Moscow was ready for the eventuality of a nuclear war "from a military-technical point of view".

He said, however, that he saw no rush towards nuclear confrontation and that Russia had never faced a need to use nuclear weapons in Ukraine.