Former national security advisor Michael Flynn officially moved to withdraw his guilty plea Tuesday, more than two years after he initially said he had lied to federal agents about his contacts with a Russian diplomat before the inauguration of President Donald Trump.

"Michael T. Flynn is innocent," his attorney, Sidney Powell, wrote in a 22-page filing in U.S. District Court in Washington, D.C.

Powell wrote that Flynn is withdrawing his plea "because of the government's bad faith, vindictiveness, and breach of the plea agreement." She also asked Judge Emmet Sullivan for a 30-day delay of Flynn's sentencing date, which is currently scheduled for Jan. 28.

Sullivan has yet to sign off on Flynn's plea withdrawal. The judge could possibly reject Flynn's motion, letting the guilty plea stand.

Former prosecutors who spoke with CNBC said it is ''nearly impossible'' to win approval for withdrawing a federal guilty plea.

Less than a week earlier, federal prosecutors had urged Sullivan to jail Flynn for up to six months, citing the "serious nature of" Flynn's "offense," and "his apparent failure to accept responsibility" for his crime.

Prosecutors had been outraged by what they called Flynn's "extraordinary" shift toward a claim of innocence in late 2019.

Their new recommendation of half-a-year locked up marked a stark reversal: Prosecutors had previously recommended that Flynn receive no jail time in recognition of his extensive help with several investigations following his guilty plea in late 2017.

Flynn was charged as part of then-special counsel Robert Mueller's investigation of Russian election interference during the 2016 presidential election. He had nearly been sentenced in December 2018, but opted to postpone that proceeding after Sullivan harshly urged him to first complete his cooperation with Mueller's probe.

"Arguably, you sold your country out," Sullivan said at that hearing.

After Sullivan granted that sentencing delay, Flynn hired Powell, who has claimed in court filings that federal prosecutors suppressed evidence that could help prove Flynn was innocent.

Sullivan last month rejected her request to compel prosecutors to hand over that voluminous evidence, saying Flynn's lawyers "failed to explain" how most of the information that had not already been turned over to them is relevant to the crime he admitted.

Joseph Tacopina, a top criminal defense attorney in New York City, said that Flynn faces very long odds in undoing his guilty plea.

"Flynn waived his right to a trial when he pled guilty and pursuant to the cooperation agreement he understood and agreed that it is the prosecutor who determines what is truthful testimony," said Tacopina, who early in his career was a state prosecutor in Brooklyn.

"He is bound by that. But he is trying to flip it on its head and say that he is the one who determines what is truthful or not truthful. It doesn't work that way once you sign a plea agreement," Tacopina said.