The Kremlin said on Wednesday that it was not sure of the veracity of a CNN article that reported U.S. President Donald Trump had once threatened to bomb Moscow to deter Russian President Vladimir Putin from attacking Ukraine.

Russian media have been reacting to Trump's growing criticism of Putin, the most recent being on Tuesday when he accused the Russian leader of peddling "bulls***" over his intentions in Ukraine, after rejecting U.S. ceasefire proposals.

The Kremlin has broken its silence on the US President's alleged threat to Moscow ahead of the Ukraine invasion.

The apparent suicide of Russia’s transportation minister brought expressions of shock and sorrow from the Kremlin but no new clues as to why Roman Starovoit might have taken his own life amid media speculation he potentially was facing corruption charges.

The Kremlin said on Tuesday that it was shocked by the sudden death of Russia's former transport minister Roman Starovoit, news of which broke hours after President Vladimir Putin had sacked him.

Former Russian Transport Minister Roman Starovoit died by suicide on Monday, just hours after Russian President Vladimir Putin fired him from the job, officials said.