U.S. President-elect Donald Trump speaks at a "Thank You USA" tour rally in Grand Rapids, Michigan, U.S. December 9, 2016. Reuters/Mike Segar A unit of the US Treasury Department that fights money laundering will provide financial records to an investigation by the Senate into possible ties between Russia and President Donald Trump and his associates, The Wall Street Journal reported on Friday, citing people familiar with the matter.

The Senate Intelligence Committee asked for the records from the Treasury's Financial Crimes Enforcement Network, or FinCEN, late last month, The Journal cited the people as saying.

One person said the records were needed to decide whether there was collusion between Trump associates and Russia during the 2016 campaign, The Journal said. It was not immediately clear what types of records were being shared.

Representatives for FinCEN and Republican Senator Richard Burr, the intelligence committee chairman, declined to comment, The Journal said.

Following the money

Trump has repeatedly denied any wrongdoing amid the Russia investigations and has railed against US intelligence agencies and lawmakers involved in the inquiries.

Sen. Ron Wyden of Oregon, who sits on the Senate Finance Committee, told The Journal that information on shell companies and property transfers would be among the types of documents pertinent to the Senate Intelligence Committee's investigation.

A Reuters review published in March found that at least 63 individuals with Russian passports or addresses have bought at least $98.4 million worth of property in seven Trump-branded luxury towers in southern Florida, according to public documents, interviews and corporate records.

LUXURY APPEAL: From left, the Trump Royale, the Trump Palace and the Trump International Beach Resort in Sunny Isles Beach, Florida. REUTERS/Joe Skipper

The full scope of Trump's labyrinthine financial affairs is not publicly known, partly because Trump has refused to release his tax returns. Throughout the 2016 presidential campaign, Trump insisted he would not publish his returns due to an Internal Revenue Service (IRS) audit. Though the IRS has said an audit would not prevent Trump from releasing his returns, he has persisted with the claim.

In recent weeks, Trump and his surrogates have indicated he has no intention to release his tax returns.

Trump's lawyers said on Friday that a review of his last 10 years of tax returns did not reflect "any income of any type from Russian sources," with some exceptions, The Associated Press reported. The news wire service was unable to independently verify the claims, which were seen as a move to allay concerns about Trump's finances amid the ongoing Russia investigation.

Donald Trump and James Comey Getty Images

Fallout over a fired FBI director

The Senate probe took on added significance after Trump dismissed FBI Director James Comey earlier this week as the bureau's inquiry began to accelerate. Trump on Friday sought to discredit Comey after 72 hours of fallout from the FBI director's firing.

Trump issued a thinly veiled threat to Comey on social media Friday morning, suggesting there may be "tapes" of conversations between the two. A source familiar with the matter told CNN on Friday that Comey is "not worried about any tapes."

Comey was expected to talk to the Senate Intelligence Committee in a closed-door meeting next week, but declined the offer on Friday. The New York Times later reported that Comey was still willing to testify before the panel, but would rather do so in a public hearing.