Durham has been working with the attorney general for "at least a couple of weeks" to examine whether federal agencies acted properly in the early stages of the investigation, which ultimately produced the lengthy report from special counsel Robert Mueller.
President Donald Trump has long called for an examination of the long probe, often calling it a "witch hunt" and saying it was politically-motivated.
Durham has been a special prosecutor the past, which includes an examination of the FBI's ties to a crime boss in Boston and CIA abuses of detainees. Durham's is the latest government investigation related to Russian interference in the 2016 U.S. presidential election. Michael Horowitz, the Justice Department's inspector general, is looking into the bureau's use of wiretaps and informants to see if they were motivated by political bias.
"I think spying did occur," Barr told a Senate committee last month. "For the same reason we're worried about foreign influence in elections ... I think spying on a political campaign, it's a big deal."
FBI director Christopher Wray has said he's not aware of any surveillance abuses by the bureau.
Durham was appointed to his post by Trump in 2017 and has been a Justice Department attorney for nearly 40 years.