"They say the International Atomic Energy Agency (IAEA) wants to come and check Ukraine's nuclear facilities. We are in favour. And it should be done as fast as possible," Putin told members of the annual Valdai Discussion Club.

The Russian president added that Kyiv is "doing everything to cover up traces of this preparation".

A dirty bomb is a conventional bomb laced with radioactive, biological or chemical materials which are spread in an explosion.

Russia has accused Ukraine of preparing such a "dirty bomb" against Moscow's troops.

"I gave (Defence Minster Sergei) Shoigu the order to call all of his colleagues and inform them" of the plan, Putin said Thursday.

Over the past week, Shoigu repeated the allegations in calls with numerous counterparts including from France, the US, the UK, China and India.

France, the US and the UK rejected the claim and NATO chief Jens Stoltenberg warned Russia may be trying to use the claim as a "pretext" for escalation.

Kyiv suspects Russia might itself use a dirty bomb in a "false flag" attack, possibly to justify use of conventional nuclear weapons by Moscow as it finds itself on the back foot in eastern and southern Ukraine.

Putin said Thursday using nuclear weapons in Ukraine would "make no sense at all to us -- either in political or military terms".

He said Ukraine and the West accused Russia of military escalation to "influence neutral countries and tell them: look at Russia! Don't cooperate!"