The US official warned that Putin’s regime could take the drastic step if his troops continue to be met with strong resistance by the brave Ukrainian people.

They told Defense One: “The [United States] has newer weapons to deter conventional conflict…Russia has nuclear weapons as part of a warfighting battle plan.”

The former official said the danger is increasing “precisely because the conflict in Ukraine is going badly”.

“Ukrainians may or may not cease and desist.

“The West may or may not continue to arm the Ukrainian insurgency and [Putin] might decide, ‘OK. I’m going to set off a bomb somewhere in western Ukraine to send a message that I have crossed the nuclear threshold, and you can follow me if you want’.

On Tuesday, CIA director William Burns told a House Intelligence Committee hearing that the Russian military contemplates using smaller tactical nuclear weapons.

Mr Burns said: “You know, Russian doctrine holds that you escalate to de-escalate, and so I think the risk would rise, according to the doctrine.”

Similarly, a former White House official told Defense One the risk of Russia using nuclear weapons is rising – largely motivated by Putin who doesn’t view the extremely destructive weapons in the same way the US does.

The source described the weapons as a “warfighting tool” to Putin.

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It comes after Kremlin officials are said to be “privately denouncing” Putin’s “clusterf*** invasion” following many Russian losses.

Asked how Russian politicians were reacting to the crisis, a source told Rustamova: “They’re carefully enunciating the word clusterf***. No one is rejoicing.

“Many understand that this is a mistake, but in the course of doing their duty they come up with explanations in order to somehow come to terms with it.”

Russia has also been accused of leaving the bodies of dead Russian soldiers in Ukraine to hide the true extent of losses, denying them a humane burial.

Scott Berrier, director of a US defence intelligence agency, said Putin has been updating his arsenal while in power, and “invested in tactical nuclear weapons”.

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Last month, Putin made the shocking announcement that he had put Russia’s nuclear forces on high alert causing anxiety and fear to spread throughout the West.

US intelligence said the “angry” Russian leader is frustrated that his invasion hasn’t gone to plan so is hurling inflammatory nuclear threats at Western nations.

Avril Haines, the director of National Intelligence, told a House Intelligence Committee meeting yesterday: “Putin’s nuclear sabre-rattling’ has put the West on notice.

“We assess Putin feels aggrieved the West does not give him proper deference and perceives this as a war he cannot afford to lose.”

She added: “But what he might be willing to accept as a victory may change over time.”

Ukraine claims to have killed nine of Putin’s military commanders and 12,000 Russian troops since the start of the invasion.