US president-elect Donald Trump has slammed White House Press Secretary Josh Earnest by describing him as a "foolish guy" who delivers a "positive message that sounds bad".

"This foolish guy, Josh Earnest, I don't know," Trump told thousands of his supporters in Hershey, Pennsylvania. "You know, having the right press secretary is so important because he's so bad the way he delivers a message. He can deliver a positive message and it sounds bad. He could say ladies and gentlemen, today we have totally defeated ISIS, and it wouldn't sound good, OK?" Trump said.

He then said that Earnest is taking orders from someone else. "Maybe he is getting his orders from somebody else?" the president-elect said hours after Earnest at his daily news conference said that Trump knew that the Russian alleged hacking and interference in general elections was helping him and hurting that of the rival Hillary Clinton Campaign.

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"It is just a fact you all have it on tape that the Republican nominee for president was encouraging Russia to hack his opponent, because he believed that would help his campaign. It is not a controversial statement. I'm not trying to be argumentative. But I am trying to acknowledge a basic fact," the White House Press Secretary told reporters at his daily news conference.

"I recognise that the defence from the Trump campaign is that he was joking. I don't think anybody at the White House thinks its funny that an adversary of the US engaged in malicious cyber activity to destabilise our democracy. That's not a joke.

"Nobody at the White House thought it was a joke. Nobody in the intelligence community thought it was a joke," he said. "I'm not aware that any members of Congress in either party that was briefed on this matter multiple times dating back to the summer thought it was a joke.

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