"Russian lies about Ukraine allegedly planning to use a 'dirty bomb' are as absurd as they are dangerous", Foreign Minister Dmytro Kuleba said on social media.

"Firstly, Ukraine is a committed (Treaty on the Non-Proliferation of Nuclear Weapons) NPT member: we neither have any 'dirty bombs', nor plan to acquire any. Secondly, Russians often accuse others of what they plan themselves."

Russia's Defence Minister Sergei Shoigu on Sunday held rare calls with NATO counterparts in which they discussed Ukraine, the Russian defence ministry said.

In calls with his British, French and Turkish counterparts, Shoigu conveyed "concerns about possible provocations by Ukraine with the use of a 'dirty bomb'".

Britain's defence ministry said in a statement that Defence Secretary Ben Wallace had "refuted" claims that Western countries sought to help Ukraine escalate the conflict.

He had also "cautioned that such allegations should not be used as a pretext for greater escalation".

Shoigu also discussed Ukraine on Sunday with Pentagon chief Lloyd Austin in their second phone call since Friday, however the Russian side did not mention the alleged "dirty bomb" provocation in its statement.