A classified briefing on Russian hacking, given to both President Barack Obama and the President-elect, included allegations that Mr Trump or his surrogates had direct contact with the Kremlin before and during the 2016 election campaign.
And the report also details "perverted sexual acts" involving prostitutes alleged to have taken place in a hotel room in Moscow. The suggestion is that the claims could have been used by Russia to compromise the incoming US President.
Mr Trump has strenuously denied the unverified allegations, which came in a two-page synopsis attached to a classified intelligence report into Russian interference in the US election. A declassified version was distributed publicly last week.
Intelligence officials said they could not independently verify the embarrassing claims, compiled by a former British spy who was hired by Mr Trump’s political opponents.
The Kremlin dismissed the report as "fake" and "total bluff" in a statement on Wednesday morning, saying it had no "compromising information" on either Mr Trump or his 2016 rival Hillary Clinton. On Tuesday night, Mr Trump's political advisor Kellyanne Conway also dismissed the claims as coming from "unnamed, unspoken sources".
FAKE NEWS - A TOTAL POLITICAL WITCH HUNT!— Donald J. Trump (@realDonaldTrump) January 11, 2017
The allegations have been circulating among intelligence agencies for some months and were in part reported upon before the election, but they have now been presented to the President and President-elect in greater detail because officials have performed checks on the former British spy and his sources and found them largely credible, CNN reported.
While stressing that the sexual claims remain unverified, BuzzFeed News published the classified two-page synopsis in full online. The site says it published the unsubstantiated allegations so Americans could make up their own minds.