Intercepted documents, financial transactions are the focus of an ongoing US investigation into possible ties between Trump advisers and Russia
A report from The New York Times published Thursday night said the counterintelligence inquiry focused on at least three advisers associated with Trump - former campaign manager, Paul Manafort, close Trump confidante Roger Stone, and former Trump adviser, Carter Page.
It was unclear whether any of the information directly connected the president-elect or his associates to Russian operatives, The Times said. The newspaper's unnamed US intelligence sources said they were talking "because they feared the new administration would obstruct their efforts."
The CIA concluded last month that hackers directed by high-level Russian officials worked to interfere in the 2016 US presidential election - ostensibly to help Trump win. Trump openly questioned the veracity of the US intelligence community's findings for weeks before conceding that Russia indeed meddled in the election.
It was unclear whether the counterintelligence efforts are part of the ongoing hacking investigation.
As The Times noted, there is a degree of uncertainty surrounding the US intelligence community's efforts because once Trump assumes the Oval Office, he will have the authority to stop or redirect some of that work.