'Kyiv is well aware that such a step would mean a guaranteed escalation to World War Three,' TASS quoted Alexander Venediktov, the deputy secretary of Russia's Security Council, as saying, Daily Mail reported.
Venediktov, who is deputy to Security Council Secretary Nikolai Patrushev, a powerful Putin ally, said he felt Ukraine's application was propaganda as the West understood the consequences of Ukrainian membership of NATO, Daily Mail reported.
Apparently, that's what they are counting on - to create informational noise and draw attention to themselves once again,' Venediktov said.
'The suicidal nature of such a step is understood by NATO members themselves,' he added.
'We must remember: a nuclear conflict will affect absolutely the whole world, not only Russia and the collective West, but every country on this planet,' Venediktov said. 'The consequences would be disastrous for all mankind.'
The warning comes after Ukrainian President Volodymyr Zelensky announced a surprise bid for fast-track membership of NATO on September 30, Daily Mail reported.
Just hours earlier, Russian President Vladimir Putin had formally proclaimed the annexation of up to 18 per cent of Ukraine.
However, Ukraine's membership bid was seen as largely symbolic, since full membership would require consent from all 30 NATO members, and ongoing territorial disputes are an obstacle for countries to join the alliance, Daily Mail reported.