Moscow has made unsubstantiated accusations that Ukraine is preparing to use an explosive laced with radioactive materials

Russian leader repeats claim Ukraine plotting to set off a 'dirty bomb' in a false flag attack as defense chief discusses allegation with his Chinese and Indian counterparts

Analyst says Russia's allegation 'just noise' for now; most believe there's little chance false flag attack could really be used as a pretext for nuke detonation

'The Ukrainians are not building a dirty bomb,' US military official says, after Moscow claims that Kyiv may deploy an unconventional device