A former British Army commander has warned that the use of nuclear weapons by Vladimir Putin in his war against Ukraine could be "devastating" in the country.
General Sir Richard Barrons, who headed up Britain's Joint Forces Command until his retirement in 2016, said that employment of weapons of mass destruction (WMD) by Russia had to be prepared for.
The Russian president has said he is prepared to use “all the means at our disposal” - including nuclear weapons - if his country is threatened, seen as a sign that he could use so-called "tactical" strikes in response to attacks on parts of Ukraine he has annexed.
Tactical nuclear weapons use smaller warheads than strategic nuclear weapons and are more likely to be used on the battlefield.
General Sir Richard said: "We absolutely should recognise that if Russia feels it is being pushed to the point of collapse we are going to have the discussion about weapons of mass destruction."
Asked what effect the weapons could have, Barrons said that the smallest warheads have an effect of 0.1 kilotonnes of TNT, but tactical nuclear missiles for battlefield use a yield of between one to 50 kilotonnes.
"The effects would be confined to Ukraine," he told the BBC on Monday. "But it would be devastating over an area of two square miles."
Asked what response he would expect from NATO if Putin decided to deploy nuclear weapons, General Sir Richard made it clear Moscow would be headed for pariah status.
Watch: Who is Vladimir Putin?
He said: "The key to the WMD issue is to make it clear to Russia, at a political and strategic level, that the policy of reaching for weapons would be a complete disaster for Russia's place in the world for a generation or more." He added that NATO would have to seek the support of China when emphasising this.
Putin announced the annexation of four more areas of Ukraine on Friday after a series of illegal referendums in Russian-held territories.
He used his speech to attack the West and defend his motives for invading Ukraine.
"The dictatorship of the Western elites targets all societies," he said. "This is a challenge to all. This complete renunciation of what it means to be human, the overthrow of faith and traditional values, and the suppression of freedom are coming to resemble a 'religion in reverse' — pure Satanism."
While Putin has insisted he is "not bluffing" over his threat to unleash nuclear destruction, reaction in the West has been mixed.
On Sunday, the UK Defence Secretary Ben Wallace said it was “highly unlikely” that Putin will use nuclear weapons in Ukraine - but warned he is not acting in a “rational” way.
In the US, Defence Secretary Lloyd Austin told CNN: “There are no checks on Mr Putin. He made the irresponsible decision to invade Ukraine, he could make another decision.”
On Monday, Ukrainian president Volodymyr Zelenskiy confirmed that Ukraine had “fully cleared” Russian forces from the key eastern city of Lyman, a day after Moscow admitted its troops had pulled out after they were encircled.
The victory is another major battlefield setback for Moscow following humiliating retreat in the Kharkiv region two weeks ago.