Russian operatives claim to have compromising personal and financial information about President-elect Donald Trump, according to US reports.
Classified documents outlining what the Russians know were presented to both President Barack Obama and Mr Trump last week by senior US intelligence chiefs, CNN says.
Some of the allegations about Mr Trump are described as sexual in nature.
It's alleged the Russians also have personal information on a number of other high-ranking US officials.
Trump has responded to the story on Wednesday by tweeting: “Fake news – a total political witch hunt.”
The documents stem from a report on Russian interference in the 2016 US election, and they include allegations that there was a continuing exchange of information between Trump insiders and the Russian government during the campaign.
But while Trump’s team was fed information to assist his campaign the dossier warns the Russians are believed to have personal information about the president-elect that compromises him.
CNN say Mr Trump's transition team repeatedly declined their requests for comment.
The two-page dossier contains allegations that came, in part, from memos compiled by a former British intelligence operative, whose past work is considered credible by US intelligence officials.
The FBI is investigating the credibility and accuracy of the allegations, which are understood to have come from Russian sources.
Previous correspondence, including memos the two-page dossier is based on, have been in circulation since 2016 and some of the allegations about Mr Trump were first published by American magazine Mother Jones a week before the US election.
US intelligence agencies investigated the former British intelligence operative and have now deemed him credible enough to include some of the information in the two-page dossier presented to Mr Obama and Mr Trump in the past few days.