US spy chiefs have informed Donald Trump that Russian operatives claim to possess deeply compromising personal and financial information about him, US media reported Tuesday on the eve of the president-elect's first press conference.

Trump denounced a “political witch hunt” after CNN reported that intelligence officials briefing him last week on allegations of Russian meddling in the US election had also given him a synopsis of the explosive and unverified claims.

“FAKE NEWS - A TOTAL POLITICAL WITCH HUNT!” the president-elect tweeted.

Intelligence chiefs last week presented America's incoming 45th president, as well as outgoing President Barack Obama, with a two-page synopsis on the potential embarrassment, according to CNN and The New York Times, who cited multiple unnamed US officials with direct knowledge of the meeting.

Obama delivered his farewell address Tuesday evening as the bombshell report was reverberating in political and diplomatic circles with just 10 days to go until Trump's inauguration.

CNN gave no details of the allegations but US media outlet Buzzfeed published, without corroborating its contents, a 35-page dossier of memos on which the synopsis is based, which had been circulating in Washington for months.

The memos describe sex videos involving prostitutes filmed during a 2013 visit by Trump to a luxury Moscow hotel, supposedly as a potential means for blackmail.

They also suggest Russian officials proposed lucrative deals in order to win influence over the Republican real estate magnate.

The dossier was originally compiled by a former British MI-6 intelligence operative hired by other US presidential contenders to do political “opposition research” on Trump in the middle of last year, according to CNN.

Trump was reportedly informed of the existence of the dossier ─ and its salacious details ─ last Friday when he received a briefing from US intelligence chiefs on alleged Russian interference in the presidential election.

The classified two-page synopsis also included allegations that there was a regular flow of information during the campaign between Trump surrogates and Russian government intermediaries.

“Nothing's been confirmed,” Trump senior aide Kellyanne Conway told NBC about the material. “They're all unnamed, unspoken sources.”

'Truly shocking'

The incendiary allegations come on the eve of Trump's first press conference since his election ─ at which he was already set to face intense scrutiny over his relationship with Russia and myriad other controversies.

The 70-year-old billionaire directly assailed Buzzfeed, re-tweeting an article that blasted the online publication for publishing the “unverifiable” dossier.

Buzzfeed said it posted the material in the interest of transparency, but its editor in chief Ben Smith acknowledged that “there is serious reason to doubt the allegations.” But Democrats were left stunned by the developments.

“If these allegations are true, allegations of coordination between Trump campaign officials and Russian intelligence officials, and allegations that the Russians have compromised President-elect Trump's independence, that would be truly shocking,” Democratic Senator Chris Coons said on CNN.

House Democrat Jared Polis took it further.

“If the reports of Trump being compromised are not true they must be refuted,” Polis posted on Twitter. “If true he should not be president.”

The Federal Bureau of Investigation was provided with the information in August, more than two months before the November 8 election.

Since then US spy agencies have checked out the former British intelligence operative and his network, and found him credible enough to include some of the information in the presentation to Trump, according to CNN.

The existence of compromising and salacious information on Trump in Russian hands had been rumoured since before the election.

'Explosive information'

The rumours gained momentum when then Senate Democratic leader Harry Reid wrote FBI Director James Comey one week before the vote.

“It has become clear that you possess explosive information about close ties and coordination between Donald Trump, his top advisers, and the Russian government,” Reid wrote in his letter.

“The public has a right to know this information.”

Comey was one of four top officials who briefed Trump Friday, along with the heads of the Directorate of National Intelligence, the Central Intelligence Agency and the National Security Agency.

Asked in a Senate hearing Tuesday about the allegations of sustained contacts between Russia and the Trump team, Comey refused to confirm or deny his agency was investigating such links.

US intelligence has already made the virtually unprecedented accusation that Russian President Vladimir Putin sought to tip the electoral scales in Trump's favour by ordering a hack of Democratic Party emails.

Trump has repeatedly dismissed the conclusion that Moscow influenced the election, while calling for a push to mend bilateral relations deeply strained during the Obama presidency.

At the weekend he condemned as “stupid” anyone opposing better relations with Moscow.