WASHINGTON — A federal judge on Tuesday set sentencing for Dec. 18 for President Donald Trump's former national security adviser Michael Flynn as prosecutors said they reserved the option of seeking prison time for Flynn, which would reverse an earlier recommendation of probation.

Assistant U.S. Attorney Brandon Van Grack said the government will file new sentencing papers as Flynn's defense team escalated its legal fight to have a court in Washington toss his prosecution because of alleged misconduct by former special counsel Robert Mueller III's Russia investigation.

Flynn pleaded guilty on Dec. 1, 2017, to lying to the FBI about contacts with then-Russian Ambassador Sergey Kislyak, becoming one of the first Trump associates to cooperate and the highest-ranking official charged in Mueller's investigation of Russian interference in the 2016 presidential election.

U.S. District Judge Emmet Sullivan set an Oct. 31 hearing to weigh Flynn's allegations that prosecutors withheld classified and other evidence they assert would help his case.

But even as he did, Sullivan pressed Flynn's team about the relevance of its claims and said both sides would have to ponder how to proceed if the government stands by its position no such evidence exists.

"Is that where this is headed ...?" Sullivan asked Flynn attorney Sidney Powell, "to say, what, he's innocent of this charge?"

Powell replied: "To say this entire prosecution should be dismissed for egregious government misconduct and suppression" of evidence potentially beneficial to Flynn.

Flynn earlier this year fired the defense team that negotiated his plea, and Powell reversed course, asking Sullivan in an Aug. 30 filing to find prosecutors in contempt for allegedly withholding information to coerce the plea from the former three-star general.

In the filing, Flynn's current lawyers accused elements of the FBI, CIA and Pentagon of trying "to smear him as an 'agent of Russia,'" leaking information regarding classified intercepts of his calls with Kislyak or engaging in other "malevolent conduct."

They also said the government had denied them security clearances to review unspecified classified documents Flynn's team contends exist that "almost certainly relate" to his case.

Prosecutors have said Flynn, 60, has finished his cooperation.

But after previously describing him as a model cooperator and recommending no prison time, Van Grack told Sullivan Tuesday that the government would not rest on its earlier sentencing submission and instead will "refile the appropriate papers" Dec. 2.

Van Grack, a former Mueller team member and one of those accused by Flynn's team of improper conduct, also said in court filings that "the government has exceeded its discovery and disclosure obligations in this matter."

He said that the government had turned over 22,000 pages of documents before Flynn's plea and "is not aware of any classified information that requires disclosures to the defendant or his counsel."

Sullivan has in the past heatedly rejected suggestions by Flynn's initial defense team that Flynn might have been duped into lying to the FBI about his conversations with Kislyak, noting Flynn had pleaded guilty and made multiple sworn admissions of wrongdoing.

"Arguably, you sold your country out," Sullivan told Flynn during Flynn's initially scheduled sentencing hearing, coincidentally held last Dec. 18. Sullivan cited Flynn's admissions that he hid the substance of talks with Kislyak and lied when he said he did not know the extent of the Turkish government's involvement in work his firm had obtained and when he claimed an op-ed he wrote for the Turkish president's benefit was done at his own initiative.

On Tuesday, Sullivan said little as Powell claimed the government has withheld evidence finding that Flynn was not an agent of the Russian government and should not be prosecuted for violating a law that bars unauthorized people from negotiating U.S. disputes with foreign governments.

Van Grack said Flynn was not charged with those offenses.

"The government has not alleged in filings in this court that the defendant is an agent of Russia. That is not part of this case," Van Grack, saying Flynn was charged and pleaded guilty to lying to FBI investigators.

He also responded to Powell's claim that prosecutors before Flynn's plea had not turned over an FBI agent's texts, which she said showed the agent working on Flynn's case was "impaired by bias" against Trump.

Van Grack told the court that Flynn's first defense team was told before his guilty pleaabout communications showing an FBI agent in the case preferred Trump's opponent, Hillary Clinton. Van Grack also told the judge prosecutors later gave Flynn's lawyers additional text messages — that had not been made public — that prosecutors believed were relevant.

Flynn's plea revealed he was in touch with senior Trump transition officials before and after his communications with the ambassador. The pre-inauguration communications with Kislyak involved efforts to blunt Obama administration policy decisions on sanctions on Russia and a United Nations resolution on Israel, according to his plea.

Flynn also admitted he did not truthfully answer on Jan. 24, days after Trump was inaugurated, when the FBI asked about the nature and extent of his conversations with the Russians.

The lies — which prosecutors said Flynn repeated to Vice President Mike Pence — ultimately cost Flynn his job as national security adviser.

Flynn's indictment and plea papers did not identify which senior Trump transition officials he consulted with, saying only that he told prosecutors a "very senior member of the Presidential Transition Team" had directed him to contact officials from foreign governments, including Russia, about the U.N. resolution.

People familiar with the contacts indicated that includes consultation with Jared Kushner, Trump's son-in-law.

Flynn also admitted that before speaking with Kislyak, he called a senior transition official at the Mar-a-Lago resort to discuss what to say about U.S. sanctions. The senior transition official is not identified in records, Mueller's final report identified the official as K.T. McFarland, a onetime Flynn deputy.

McFarland, who initially denied to FBI agents ever talking to Flynn about sanctions in the call, subsequently revised her statement and told investigators they may have discussed sanctions, The Washington Post reported.