US officials have warned that Russia could lash out in anger at Ukraine's fierce and courageous resistance by using small nuclear weapons, according to reports.
It is feared the despot may decide to take the drastic step if Russian forces continue to meet fierce resistance from the defenders, according to the Mail.
Speaking at a House Intelligence Commitee hearing yesterday CIA director William Burns said the Russian military doctrine contemplates the use of smaller tactical nuclear weapons.
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."
A former senior White House official familiar with Russian nuclear security issues told Defense One that the risk of a Russian first nuclear use is rising - largely motivated by Putin not viewing such weapons in the same way as the US or even the former Soviet Union.
The source, who described these weapons as a "warfighting tool" to Putin, 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 added the danger is increasing “precisely because the conflict in Ukraine is going badly” - and outlined a scenario in which Putin consolidates some gains in southern Ukraine but fails to install a new puppet regime.
They said: “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.”
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Meanwhile, Kremlin officials are said to be "privately denouncing" Putin’s "clusterf**k invasion" amid heavy Russian losses.
Asked how Russian politicians were reacting to the crisis, a source told Rustamova: "They're carefully enunciating the word clusterf**k. 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."
Lieutenant General Scott Berrier, director of the Pentagon’s Defense Intelligence Agency, said Russia under Putin has been working overtime to modernise its weaponry, particularly smaller-yield nuclear weapons.
Putin has "invested in tactical nuclear weapons," Berrier said.
He added: "I believe that he thinks that gives him an asymmetric advantage."
The Russian leader took the shocking step to put Russia's nuclear forces on high alert last month - which immediately put the West on notice.
US intelligence chiefs on Tuesday branded Putin an "angry" and isolated leader grappling for global sway.
They added he is frustrated about how his Ukraine invasion has not gone to plan and is lobbing provocative nuclear threats at the West.
Some intelligence experts even expressed concerns that, in a worst-case scenario, Putin could be tempted to order the deployment of mini-nukes on a city.
Speaking at a House Intelligence Committee hearing yesterday, Avril Haines, the director of National Intelligence, said: "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."
Russia has been accused of not taking the bodies of dead soldiers home to hide the country's true death toll in Ukraine.
Iryna Vereshchuk, Deputy Prime Minister of Ukraine and Minister for Reintegration of Temporary Occupied Territories, said Russian leader Vladimir Putin is hiding the scale of the war from families during an all-Ukrainian telethon.
She said: "Obviously, believing that the bodies of servicemen of the Russian Federation are not worthy to return to their homeland and be buried humanely.
"At the same time, the Cabinet of Ministers of Ukraine has developed and approved a step-by-step procedure for their transfer.
"They leave their dead here in Ukraine without the right to be buried in the Russian Federation for one purpose: to prevent Russian mothers, wives and daughters from learning about the true scale of the war waged by Vladimir Putin, the thousands and thousands killed and the collapse that Russia is waiting if this war continues for some time to come.
"Such atrocities against even our people, of course, shock us. But they do not stop our army. We are on our land."
Nine of Vladimir Putin’s military commanders have been wiped out so far in Russia’s invasion of Ukraine.
The commanders are among the 12,000 Russian troops Ukraine now claims it has killed.