Donald Trump was replying to unsubstantiated allegations that his election team colluded with Russia and there were salacious videos of his private life.
Intelligence agencies considered the claims relevant enough to brief both President-elect Donald Trump and President Barack Obama last week.
Donald Trump also said for the first time that Russia was behind hacking attacks.
He went on to confirm he was handing total control of his businesses to his two sons.
His first briefing was scheduled in order for Donald Trump to give details about his business affairs, but was dominated by the allegations of compromising material.
Donald Trump said the information “should never have entered paper… it should never have been released”.
“It’s all fake news, it’s phoney stuff, it didn’t happen,” he said, adding that “sick people” had “put that crap together… it’s an absolute disgrace”.
Donald Trump thanked the news organizations that chose not to run with the claims, which have been circulating for months.
He said he could not talk about what he heard in last week’s intelligence agency briefing, but said there had been “many witnesses” there and that it would be a “tremendous blot” on the reputation of intelligence agencies if they had been responsible for leaking the details.
“That’s something that Nazi Germany would have done,” he said.
In response White House spokesman Josh Earnest said it was “deeply misguided for anybody, at any level, to question the integrity and motives of the patriots” in the nation’s intelligence agencies.
A 35-page dossier of allegations has been published in full on Buzzfeed and reported by CNN.
Donald Trump called Buzzfeed a “failing pile of garbage” and accused CNN of “going out of their way to build it up”.
The allegations claim Russia has damaging information about Donald Trump’s business interests, and salacious video evidence of his private life, including claims of using prostitutes at the Ritz-Carlton hotel in Moscow.
Denying any such claims, Donald Trump said that as a high-profile person he was extremely cautious about all that he did when travelling abroad.
Russia has also strongly denied the allegations.
President Vladimir Putin’s spokesman, Dmitry Peskov, said they were “pulp fiction” and a “clear attempt to damage relations”.
Donald Trump said he “respected” Vladimir Putin for putting out a statement.
He was also asked about the hacking scandal that dominated the US election campaign, with the intelligences concluding Russia was behind the hacking of Democratic Party emails.
Donald Trump said for the first time “I think it was Russia”, but added that “we get hacked by other people”.
The president-elect said: “We talk about the hacking and hacking’s bad and it shouldn’t be done.”
But he added: “Look at the things that were hacked, look at what was learned from that hacking… Hillary Clinton got the questions to the debate and didn’t report it.”
Donald Trump added: “If Putin likes Donald Trump, I consider that an asset, not a liability.”
He did not answer directly when asked whether his team had communicated with Russia during the election campaign, but he did say that any hacking by Vladimir Putin must stop.
“He shouldn’t be doing it. He won’t be doing it.”
Before today’s briefing, the Trump team acted to dismiss news of the compromising material.
Michael Cohen, a lawyer to Donald Trump named in the 35-page dossier, denied a specific claim that he went to Prague in August or September 2016 to meet Kremlin representatives to talk about the hacking.
He tweeted: “I’ve never been to Prague in my life. #fakenews.”
Reince Priebus, Donald Trump’s chief of staff, called the dossier report “phoney baloney garbage”.
US media suggest the alleged salacious videos were prepared as “kompromat” – material collected about a politician or public figure in order to create a threat of negative publicity, if needed.
The allegations began circulating in political and media circles in recent months. The existence of the documents was first reported by Mother Jones in October 2016.
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