MOSCOW - Russian President Vladimir Putin's Victory Day speech can be interpreted as an "encouraging" sign he is stepping back from the catastrophic consequences of launching nuclear weapons, experts have said.

Western officials had warned prior to the speech that the Russian president could use the opportunity to instigate a mass mobilisation of Russian troops; declare a global war on Nazis; or even raise the threat of using nuclear weapons.

Putin and Kremlin officials have issued a number of nuclear threats in the two months since invading Ukraine, but the Russian leader stopped short of raising further tensions.

Experts described the speech as a "professional performance" that showed no "potential craziness" that Western officials have been concerned about.

Former UK ambassador to Russia Sir Tony Brenton told Sky News Putin had recently shown "disturbing signs" of "losing it", in his speeches surrounding the war, but the speech today was "coherent" and a "very professional performance".

He added the speech had: "Pushed all the right patriotic buttons in the Russian political atmosphere".

He added: "It is rather encouraging that it leaves me with the feeling that we are dealing with a rational individual there with whom hopefully in time it will be possible to do a sensible deal to bring this whole mess to an end."

In the speech, Putin accused the West of planning to invade the Donbas region in the south of Ukraine.

He said: "In December last year, we proposed the conclusion of an agreement on security guarantees. Russia called on the West to enter an honest dialogue, in search of reasonable compromise solutions, to take each other’s interests into account. It was all in vain.

"Nato countries did not want to listen to us, meaning that they in fact had entirely different plans, and we saw this.

"Openly, preparations were underway for another punitive operation in Donbas, the invasion of our historical lands, including Crimea.

"In Kyiv, they announced the possible acquisition of nuclear weapons, the Nato bloc began actively taking military control of territories adjacent to ours.

"As such, an absolutely unacceptable threat to us was systematically created, and moreover directly on our borders."

Lord Dannatt, a retired British Army general, added: "The Cold War and the nuclear standoff during the Cold War worked because both sides were rational. Both sides understood the catastrophic consequences of the use of nuclear weapons. So they didn't do it.

"It's the irrationality of the potential craziness of Putin that is the real worry, particularly if he's not well. Now, he looks pretty healthy to me this morning."