WASHINGTON – A federal judge postponed sentencing Tuesday for Michael Flynn, President Donald Trump's former national security adviser, after warning he might be incarcerated for lying to the FBI about Russia contacts.

Prosecutors and defense lawyers had each recommended no prison time because Flynn, a former Army lieutenant general, cooperated with Justice Department special counsel Robert Mueller.

But U.S. District Court Judge Emmet Sullivan asked prosecutors whether Flynn's crime amounted to treason. Prosecutors said they hadn't brought such charges.

“Arguably, you sold your country out,” Sullivan told a grim-faced Flynn. “I'm not hiding my disgust, my disdain.”

Sullivan also warned that he may consider sentencing Flynn to “a term of incarceration." Sullivan set a status report in March. Late Tuesday, the judge ordered that Flynn be required to stay within 50 miles of the District of Columbia and would have to surrender his passport.

Flynn faces a maximum punishment of five years in prison, three years of supervised release and a $250,000 fine.

In requesting the postponement, Flynn attorney Robert Kelner said his “client has held nothing back” in cooperating with prosecutors. But Kelner acknowledged the judge’s earlier cautions about proceeding to sentencing while Flynn’s cooperation was likely not yet complete.

Kelner said Flynn would likely be called to testify at future trials of two former business associates accused of illegal lobbying on behalf of the Turkish government.

“I’m not promising anything,” Sullivan told Kelner. “The court was just being upfront with you.”

Prosecutor Brandon Van Grack said the government’s recommendation for leniency was warranted, saying that Flynn had “taken full responsibility for his action.”

Prosecutors said it was possible Flynn's further assistance would be needed in ongoing investigations.

As part of his plea, Flynn also had admitted to lying about Turkish lobbying and research work. He belatedly registered with the Justice Department as a foreign agent for the work weeks after he left the White House.

On Monday, federal prosecutors in Virginia charged two of Flynn's business associates in an illegal, covert effort to conceal the government of Turkey's effort to win the extradition of a Turkish cleric living in the United States.

Absent the plea agreement, Van Grack said Flynn likely would have charged in that case.

Sullivan adjourned the extraordinary session with one additional comment: “happy holidays.”

Flynn, accompanied by his wife, left the courthouse, walking through a gantlet of protesters to a waiting car without comment.

The decision to postpone sentencing came after Sullivan ordered a 15-minute recess, to allow Flynn to confer with his lawyers.

“This is a very serious offense,” Sullivan said, noting that Flynn made the false statements to the FBI on “the premises of the White House.”

But after the break, Sullivan said that he had not meant to imply that Flynn had committed treason when he earlier asked prosecutors whether they had considered bringing such an offense.

“Don’t read too much into my questions,” the judge told the court.

The sentencing was postponed after Flynn's defense lawyers filed a memo that agreed with prosecutors that deserved no prison time, but offered a new account of the Jan. 24, 2017, interview with FBI agents.

Flynn gave the interview without a lawyer present and lied about his contacts with Russia ambassador Sergey Kislyak. Before the interview, his attorneys said, FBI officials had decided that they would not warn Flynn about the criminal consequences for lying to federal agents.

"One of the agents reported that General Flynn was 'unguarded' during the interview and 'clearly saw the FBI agents as allies,' " the Flynn document stated.

Sarah Sanders, the White House press secretary, suggested Tuesday on Fox News Channel's America's Newsroom that FBI violated protocols in interviewing Flynn.

“Look, we’re arguing that he was certainly ambushed and that the FBI, that we know, had clear political bias, we’ve seen that time and time again," Sanders said.

After the hearing, Sanders said the administration isn’t aware of anything Flynn did that constituted treason.

“The delay is something between Gen. Flynn and the courts,” she said at the White House briefing. “The things that may have taken place, that’s for the judge to make that determination."

Sanders said Flynn's guilty plea didn't deal with Trump.

“Maybe he did do those things, but that doesn’t have anything to do with the president directly,” Sanders said.

Prosecutors and Flynn's defense team told the judge they weren't challenging the interview or withdrawing his guilty plea.

Flynn told the judge that he had no intention of challenging the interview; he knew it was a crime to lie to the FBI and did not wish to withdraw his plea.

“General Flynn fully accepts responsibility,” attorney Robert Kelner told the judge, adding that his client was not suggesting that he had been entrapped by the FBI during the January 2017 interview.

Citing Flynn's "substantial" assistance to the Russia investigation and two other federal inquiries, Mueller's prosecutors earlier this month recommended that Flynn serve no prison time.

Flynn, 60, has met with investigators 19 times since pleading guilty related to his communications with the Russian ambassador during the run-up to Trump's inauguration.

Contributing: John Fritze and David Jackson