WASHINGTON — In an extraordinary move, the Department of Justice in the United States has decided to drop the criminal charges against Former National Security Adviser Michael Flynn.

Flynn, a close aide of US President Donald Trump, was convicted during special counsel Robert Mueller's investigation into alleged Russian election interference.

He had pleaded guilty to lying to FBI agents about his conversations with Russia’s ambassador to the US.

The move comes as Flynn was trying to withdraw the guilty plea on the claim that federal prosecutors had withheld potentially exculpatory material from him and his lawyers.

In court documents filed on Thursday, the DoJ said it was dropping the case "after a considered review of all the facts and circumstances of this case, including newly discovered and disclosed information."

The DoJ said the interview between investigators and Flynn in January 2017 was "unjustified" and not conducted on a "legitimate investigative basis".

It also said it could not prove beyond reasonable doubt that Flynn had lied, and said that after the interview, FBI agents had "expressed uncertainty as to whether Flynn had lied".

The U.S. attorney reviewing the Flynn case, Jeff Jensen, recommended the move to Attorney General William Barr last week and formalized the recommendation in a document this week.

"Through the course of my review of General Flynn's case, I concluded the proper and just course was to dismiss the case," Jensen said in a statement. "I briefed Attorney General Barr on my findings, advised him on these conclusions, and he agreed."

Reacting to the DoJ’s decision, President Trump said he was "very happy for General Flynn".

"He was an innocent man," the president said. "He was targeted in order to try and take down a president."

"I hope a lot of people are going to pay a big price. They're scum."

Meanwhile, former FBI director James Comey, who has been a critic of the president since he was fired in May 2017, tweeted that the justice department "has lost its way".

"But, career people: please stay because America needs you. The country is hungry for honest, competent leadership." — Agencies