The Internal Revenue Service is providing information to special counsel Robert Mueller about Trump campaign officials as investigators press forward with their Russia probe, according to a report.

The IRS Criminal Investigation division is sharing details about campaign figures, including former campaign chairman Paul Manafort and former White House national security adviser Mike Flynn, a source told CNN.

Mueller asked for assistance from the IRS in August as his team looked into possible tax and financial crimes committed in particular by Manafort. Manafort has denied any wrongdoing specifically regarding payments for work he conducted in Ukraine, funds held in offshore, tax-haven accounts and certain real estate deals.

But the IRS and Mueller disagreed over the scope of Mueller's request as his investigation spans 11 years, according to a search warrant cited by CNN.

The two parties, however, came to an agreement after working with Treasury Department staff.

The IRS holds tax-return related items like property and banking records but disclosure is governed by Title 26 of the U.S. Code, which requires a grand jury subpoena.

The IRS has also been collaborating with the FBI since the election over allegations Manafort may have laundered money and committed tax fraud, CNN added.