An order by Russian President Vladimir Putin to strike Ukraine or the West with nuclear weapons would be ignored by his top commanders, a senior investigative journalist has said, as per media reports.

Many leading military and security officials as well as oligarch cronies believe Putin to be dying or gravely ill, said Christo Grozev, who is an expert on Russian affairs and is associated with the Bellingcat open-source research group, Daily Mail reported.

Believing that Putin could soon die, his inner circle would not risk being hauled before a modern equivalent of the Nuremberg trials for unleashing Armageddon, nor would they obey a Putin order to kill opposition foes, Grozev claimed.

Grozev said: "I can't speak without information, but we know that oligarchs from his closest circle claim (that Putin is ill).

"We also know that the Lubyanka (secret service FSB) sent a letter about a month ago to all regional FSB chiefs. It said: 'If you hear about him having a very serious illness, we insist you do not pay attention.'

"So they all thought this means the exact opposite."

The Russian President placed Moscow's nuclear forces on high alert shortly after his invasion of Ukraine began on February 24, raising fears he could press the button as the war in Ukraine continues to go against him, Daily Mail reported.

And amid increasing Western support to Ukraine, Putin has made thinly veiled threats hinting at a willingness to deploy Russia's tactical nuclear weapons, which Russian military doctrine holds can be used to force an adversary to retreat.

Meanwhile, Russia has increasingly resorted to nuclear saber-rattling as the war in Ukraine has stumbled, with state media last week issuing near-daily threats - including one to wipe out the UK and Ireland with a "nuclear tidal wave". (IANS)