FORMER White House communications director Anthony Scaramucci has called US President Donald Trump “a liar” and that he “should probably dial down the lying.”

Mr Scaramucci, who has been broadly complimentary of Mr Trump since leaving his post after just 10 days in the job, told CNN that the president “likes it” when the media calls him a liar because it gets people talking.

Mr Trump had said “unknown Middle Easterners” are travelling in a migrant caravan heading north to the United States from Central America, but then admitted “there’s no proof of anything.”

Mr Scaramucci, who is currently promoting his new book, Trump: The Blue-Collar President, said the president was “like a rascal, like a scoundrel” for spreading lies.

“I asked you what do you call someone who likes to lie? You said a scoundrel,” CNN’s John Berman replied. “Another thing you could call someone who likes to lie is a liar. Is he a liar?”

“OK, well we both know that he’s telling lies. So if you want me to say he’s a liar, I’m happy to say he’s a liar,” Mr Scaramucci said. “Nobody should lie. I’m not a big believer in lying. But politicians happen to lie.”

Addressing Mr Trump directly, Mr Scaramucci said “you’re a politician now, so politicians lie when their lips are moving, and so all these people lie. But you should probably dial down the lying because you don’t need to. You’re doing a great job for the country. So dial that down, and you’ll be doing a lot better.”

Mr Trump has been under fire this week for revving up his base ahead of the November 6 midterm elections, stoking outrage for calling himself a “nationalist”.

While polls expect the Republicans to lose seats in the midterms, Mr Trump’s popularity is at its highest point since he was elected.

A NBC News/Wall Street Journal poll found that 47 per cent of respondents approve of the job Mr Trump is doing as president, while 49 per cent disapprove.

That represents a major jump in the president’s popularity; the same poll found him with a 39 per cent approval rating six months ago.