WASHINGTON (Reuters) - U.S. prosecutors on Tuesday accused President Donald Trump’s former national security adviser Michael Flynn of making “an extraordinary reversal” to try to undo his sworn admission that he lied to former Special Counsel Robert Mueller’s investigators about his contacts with Russia.

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Federal prosecutors asked U.S. District Judge Emmet Sullivan for the opportunity to oppose a bid filed by Flynn’s lawyers last week to have the case dismissed - even though Flynn pleaded guilty in 2017 - because of alleged prosecutorial misconduct. Sullivan is scheduled to sentence Flynn on Dec. 18.

The retired Army lieutenant general and former Trump campaign adviser has pleaded guilty to lying to FBI agents about his 2016 conversations with Sergey Kislyak, then-Russian ambassador to the United States.

Flynn was one of several former Trump aides to plead guilty or be convicted at trial in Mueller’s investigation, which detailed Moscow’s interference in the 2016 U.S. election to boost Trump’s candidacy as well as numerous contacts between his campaign and Russia.

“In an extraordinary reversal, the defendant now claims that he is innocent of the criminal charge in this case,” prosecutors wrote in a filing to Sullivan.

“He makes this claim despite having admitted his guilt, under oath, before two federal judges,” the prosecutors added.

Defense attorneys last week abruptly made fresh claims that “high-ranking FBI officials orchestrated an ambush-interview” of Flynn in 2017 for the “purpose of trapping him into making statements they could allege as false.”

Flynn’s lawyers also accused the FBI of suppressing and fabricating interview notes from agents, and asked the judge to dismiss “the entire prosecution” and hold the government in contempt for failing to turn over exculpatory evidence prior to Flynn’s guilty plea.

Sullivan gave prosecutors until Friday to respond to Flynn’s allegations of misconduct.

At a sentencing hearing in December 2018, Sullivan excoriated Flynn for lying to investigators, and accused him of selling out the United States.

Sullivan at the time gave Flynn the option to have his sentencing delayed so he could fully cooperate with any pending investigations to help bolster his case for leniency, including testifying in the Virginia trial of his former business partner Bijan Rafiekian on charges of illegally lobbying for Turkey.

In June, Flynn dismissed his former lawyers and tapped Sidney Powell, a frequent guest on Fox News whose website sells “Creeps on a Mission” T-shirts featuring images of Mueller, former FBI Director James Comey and other Justice Department officials.

Prosecutors decided not to call Flynn as a witness in the Rafiekian trial amid a disagreement over whether Flynn had “knowingly” submitted false statements to the Justice Department when retroactively registering as a lobbyist for Turkey.

A jury convicted Rafiekian, but the judge in the case overturned the verdict, ruling that prosecutors had failed to prove their case.