Gen HR McMaster told the BBC that Moscow used propaganda and disinformation against democracies. He said Russia's alleged meddling in US elections was "certainly" a national security threat.

He was speaking after President Trump's new national security policy labelled Russia and China "rival powers”.

Gen McMaster told the BBC's Yalda Hakim: "We have to look at what Russia's actually doing. Of course we have to counter Russia's destabilising behaviour, and the sophisticated campaigns of propaganda and disinformation.”

Those were "efforts to polarise communities and pit them against each other, especially in the democratic world and free and open societies", he added, saying that the intent was to "weaken their popular will and their resolve”.

"I believe that Russia is engaged in a very sophisticated campaign of subversion to affect our confidence in democratic institutions, in democratic processes - including elections.”