A former British agent, who compiled claims about Donald Trump, has fled his home fearing for his life.
America's Intelligence Community has denied that the unverified report came from them.
It has already led to embarrassment for the President elect who has been forced to deny a sex scandal.
Christopher Steele, 52, who runs London-based Orbis Business Intelligence, was named in reports as having compiled the file on Mr Trump.
The 35-page dossier contains unverified allegations that Russian security officials have compromising material on Mr Trump that could be used to blackmail him.
Mr Steele, a former MI6 officer, is one of two directors of Orbis, according to Companies House, along with Christopher Burrows, 58.
According to the Wall Street Journal (WSJ) Mr Steele has repeatedly declined requests for interviews in recent weeks, with an intermediary telling the newspaper the subject was "too hot".
A neighbour said he was away for a few days, the WSJ said.
The Telegraph said Mr Steele fled his home on Wednesday morning as it became clear his name would become public, and that he now feared a backlash from Moscow.
Mr Burrows refused to "confirm or deny" that Orbis, a corporate intelligence company, had produced the report, the WSJ said.
Orbis, which was founded in 2009 by former British intelligence professionals, has a "global network" of experts and "prominent business figures", according to its website.
It says: "We provide strategic advice, mount intelligence-gathering operations and conduct complex, often cross-border investigations."
The firm, based in Grosvenor Gardens, close to London's upmarket Belgravia area, says it "draws on extensive experience at boardroom level in government, multilateral diplomacy and international business to develop bespoke solutions for clients".
"Our tailored approach means the directors are closely involved in the execution and detail of every project, supported by an in-house team of experienced investigators and professional intelligence analysts," it says.
Mr Burrows formerly worked for the Foreign and Commonwealth Office as a counsellor, according to his LinedkIn profile, with postings to Brussels and Delhi in the early 2000s.
The dossier has been circulating in Washington for some time as media organisations, uncertain of its credibility, held back from publication.
Both Mr Trump and US president Barack Obama had been briefed on its contents and Mr Trump has suggested American intelligence agencies may be responsible for its release.
In a press conference in New York on Wednesday that was dramatic and at times ill-tempered, the president-elect branded the dossier "fake news" and said it would be a "tremendous blot" on the agencies' reputations if they were shown to have leaked it.
In the hours before his appearance, Mr Trump issued a series of tweets in which he denounced the document as "A COMPLETE AND TOTAL FABRICATION, UTTER NONSENSE".
"Intelligence agencies should never have allowed this fake news to 'leak' into the public. One last shot at me. Are we living in Nazi Germany?" he tweeted.
Russian president Vladimir Putin's spokesman Dmitry Peskov said the reports were "complete fabrication and utter nonsense" and the Russian government "does not engage in collecting compromising material".
Standing in front of a row of US flags, Mr Trump blamed the creation of the dossier on his political opponents, who he said had "got together - sick people - and they put that crap together".
Some of the more lurid details of the allegations were highly improbable because he was a "germophobe" who hated uncleanliness, he said, adding that he was very aware of the danger that hotel rooms may contain hidden cameras.
He thanked media organisations which declined to publish the "phoney stuff", saying: "They looked at that nonsense that was released by maybe the intelligence agencies - who knows, but maybe the intelligence agencies - which would be a tremendous blot on their record if they in fact did that, a tremendous blot.
"A thing like that should never have been written, it should never have been had and it should certainly never have been released."
Mr Trump insisted Moscow had "no leverage" over him as he had "no deals, no loans, no nothing" with Russia.
US director of national intelligence James Clapper said he had told Mr Trump that the leak did not come from the government's intelligence community.
Mr Clapper also said he told the president-elect that the US agencies had "not made any judgment that the information in this document is reliable".
Mr Steele's house in the village of Runfold, outside Farnham, Surrey, was empty on Thursday morning.
Next door neighbour Mike Hopper said Mr Steele had lived there for about 18 months with his wife and four children.
Mr Hopper, who is looking after the family's three cats, said his neighbour appeared "normal" when he left on Wednesday morning.
"He did not say where he was going or when he was coming back," he added.
Mr Hopper said it was a "fairly quiet neighbourhood" and he did not know anything about the claims until he read the newspaper