MAD Vlad Putin has already tried to detonate a nuke and may have been "sabotaged" by his own top brass, insiders claim.
The desperate tyrant, 70, is feared by Nato to have his finger inching closer to the trigger ready to launch a nuclear show of force.
The mounting concerns prompted Defence Secretary Ben Wallace to cancel his plans and jet to Washington for crisis talks this week.
Analysts feared Putin would detonate a warhead in the Black Sea, potentially unleashing tsunamis and a poisonous gas cloud.
It was also claimed plans were under way to test fire a tactical nuke in the Arctic before launching one on the battlefield in Ukraine.
Recent days have seen a number of Notam messages - short notice warnings to aircraft - and Russian navigation warnings indicating live fire drills in the Barents Sea near the border with Norway.
Read more on Russia
It is the same area where Russia's giant "city killer" Belgorod submarine armed with nuclear torpedoes was spotted days ago.
The warnings last until Saturday, although there have reportedly been few indications of major testing so far.
Meanwhile reports claim Putin ordered two nuclear tests earlier this month which did not in fact take place.
Insiders claim the launches were scuppered by "technical failure" or even by the reluctance of military chiefs.
Most read in News
This could be a sign Putin's authority is evaporating, said Varlery Solovey, former professor at Moscow’s prestigious Institute of International Relations, a training school for spies and diplomats.
He said: “Putin’s decision on the use of tactical nuclear weapons [in the Ukraine conflict] would no doubt face resistance.
“I don't know how effective the resistance will be, but I will indicate nuclear tests were supposed to be held over the past two weeks - one in the Barents sea, underwater, and the second underground, in Arkhangelsk region.
“Both times the tests were not held.
“The reason is that before the launch, or more accurately, before the use of tactical nuclear weapons, it is necessary to make sure these weapons are fully operable.
“They had to be tested.”
Solovey, an expert on the president and his inner circle, claimed Putin has made a decision in principle to use nuclear weapons.
But both the recent tests Putin ordered were “disrupted”, he claimed.
He went on: “The president got reports that there was an emergency situation, that it didn't work out” - implying technical failings.
“But the thing is, once is an accident, twice is a coincidence.
“If the third tests end the same way, with nothing, [it will look like] sabotage…not fulfilling the orders of the chief commander.”
This would show the "dissolution of [Putin’s] authority, of Russia's executive power”, he said.
'Increased threat'
His comments echoed reports on the General SVR Telegram channel, which claims to publish information from a Kremlin insider.
It said a nuclear test was ordered by Putin for October 13 and prepared “in strict secrecy”.
But the Kremlin leader “was informed about the need to postpone the date and time of the test".
It added: “Allegedly they did not have time to properly prepare.
“This is the second time a nuclear test has been postponed in the past two weeks.”
A nuclear test - even in an unpopulated area - would be a major escalation and heighten fears of all-out nuclear conflict.
Earlier this week Mr Wallace cancelled giving evidence to MPs at short notice and flew to the US capital to talk to his American counterparts.
A security source told The Sun: “The threat has increased recently.”
And Armed Forces Minister James Heappey admitted: “We are at a time when these sorts of conversations are necessary”.
The boss of spy agency GCQH said his eavesdroppers are closely monitoring for any signs Putin might launch a nuke.
And this week two RAF fighters escorted a "nuke sniffer" surveillance plane over the Black Sea near Crimea.
The RC-135W "soaks up" enemy signals and can test the atmosphere for evidence of radioactivity.
Western officials warn Putin and his generals are growing increasingly desperate after seismic battlefield losses in Ukraine and “significant failures of military leadership”.
READ MORE SUN STORIES
Read More on The Sun
Putin said last month that Moscow was ready to use nuclear weapons to defend its “territorial integrity” - including the illegally annexed regions of Ukraine.
US President Joe Biden has warned the world is closer to Armageddon than at any time since the 1962 Cuban Missile Crisis.