President Donald Trump’s former National Security Adviser Michael Flynn leaves the E. Barrett Prettyman U.S. Courthouse on June 24, 2019 in Washington, DC.

Attorney General William Barr has ordered a review by an outside prosecutor of the criminal case against President Donald Trump's first national security advisor, Michael Flynn, who is awaiting sentencing for lying to FBI agents.

Barr — who has come under fire this week for easing career prosecutors' sentencing recommendation for Trump's friend Roger Stone — asked the U.S. attorney for the Eastern District of Missouri, Jeffrey Jensen, to look into Flynn's interview by the FBI, which led to his prosecution in Washington, people familiar with the inquiry told NBC News.

The inquiry began within the past month, they said.

The New York Times reported earlier Friday that Barr had asked Jensen "to scrutinize" Flynn's case, a move that the newspaper noted was "highly unusual and could trigger more accusations of political interference by top Justice Department officials into the work of career prosecutors."

Flynn originally was charged by special counsel Robert Mueller, who was tasked by the Justice Department with investigating Russian interference in the 2016 presidential election.

Mueller has since left that post, and Flynn's case is being handled by the U.S. Attorney's Office for Washington, which is part of the Justice Department. Barr is the department's top official.

A Justice Department spokeswoman did not immediately respond to a request for comment about the review of Flynn's case.