Russian operatives claim they have compromising personal and financial information about President-elect Donald Trump, intel officials revealed in classified documents presented to Trump and President Barack Obama last week. The allegations partly came from memos collected by a former British intelligence operative.

According to CNN, the FBI is investigating the credibility and accuracy of the allegations, which are based on information from Russian sources. The agency has not confirmed essential details about Trump in the memos.

Four senior US intelligence chiefs — Director of National Intelligence James Clapper, FBI DirectorJames Comey, CIA Director John Brennan and NSA Director Admiral Mike Rogers — presented the classified briefings to Obama and Trump. The allegations were included in a two-page synopsis appended to a report commissioned by Obama on Russia's interference in the election.

Officials included the synopsis to make Trump aware that the allegations involving him were circulating around intelligence agencies, CNN reported. The synopsis also proved that Russia had information potentially damaging to both Republicans and Democrats, but chose to only release information harmful to Democrats and their nominee Hillary Clinton.

Two national security officials told CNN that the synopsis also included allegations that there was a continuous exchange of information between Trump surrogates and operatives for the Russian government during the campaign. Allegations about communications between Trump's campaign and Russia prompted former Senate Minority Leader Harry Reid to write to Comey in October.

Earlier on Tuesday (10 January), NPR's Moscow correspondent Lucian Kim tweeted that an exiled Russian politician claimed Russia would blackmail Trump by threatening to publish proof they worked to help him win the election.

Trump's transition team has not responded to requests for comments from IBTimes UK.

The two-page synopsis is drawn from a 35-page compilation of memos, which have not been confirmed or verified. According to CNN, the memos began as opposition research commissioned first by anti-Trump Republicans and then Democrats. The memos, which were published in full by BuzzFeed News, have circulated as far back as last summer.

While many of the memos have made the rounds among government officials, intelligence agencies and journalists for months, the US intelligence community has now found the former British intelligence operative and his source network throughout Europe to be credible enough to include in the briefings with the president and president-elect.

A summary of the memos regarding Trump were also given to the top four Congressional leaders, chairmen and ranking members of the House and Senate intelligence committees. The summary was considered so classified that it was only distributed to Obama, Trump and the eight Congressional leaders.

CNN also reported that Arizona Senator John McCain gave a full copy of the memos - dated through December 2016 - to Comey on 9 December. However, national security officials said the FBI already had a set of memos compiled up to August 2016, when the former MI6 agent gave them to an FBI official in Rome.