They told Reuters the claims, which one called "unsubstantiated," were contained in a two-page memo appended to a report on Russian interference in the 2016 election that US intelligence officials presented to Trump and President Barack Obama last week.
Trump responded on Tuesday evening in a tweet calling the reports: "FAKE NEWS - A TOTAL POLITICAL WITCH HUNT!" The Trump transition team did not immediately respond to a request for comment. One of the officials, both of whom requested anonymity to discuss classified matters, said the Federal Bureau of Investigation and other US agencies are continuing to investigate the credibility and accuracy of the claims.
They are included in opposition research reports made available last year to Democrats and US officials by a former British intelligence official, most of whose past work US officials consider credible.