US District Judge Emmet G. Sullivan has placed some travel restrictions on Michael Flynn as he waits to be sentenced for lying to the FBI.

Starting on January 4, Flynn cannot travel more than 50 miles from Washington, DC, and he must surrender his passport.

For nearly a year, Flynn has been cooperating with the special counsel Robert Mueller's office's investigation into Russian interference in the 2016 US election and possible collusion with the President Donald Trump's campaign.

As Michael Flynn waits to be sentenced for lying to the FBI, the judge presiding over his case placed new limits on his movements, which are set to take effect in January.

At a Tuesday hearing Flynn's lawyers asked to delay his sentencing. Judge Emmet G. Sullivan agreed, and asked Flynn if he wanted to withdraw his guilty plea. Flynn declined.

During the proceedings, the judge issued a strong rebuke against Flynn, telling him that "his crime is very serious."

"Not only did you lie to the FBI, you lied to senior officials in the incoming administration," Sullivan said.

Following the hearing, Sullivan added travel restrictions to Flynn in an electronic filing.

Starting on January 4, 2019, Flynn cannot travel more than 50 miles from Washington, DC, and he must surrender his passport. If Flynn wishes to "travel outside that area, he is directed to file a motion seeking leave of Court," the filing says. Previously planned international travel was approved.

Flynn pleaded guilty last year to lying to the FBI about his conversations with then-Russian ambassador to the United States Sergey Kislyak. He also lied about his lobbying work for the Turkish government.

For nearly a year, Flynn has been cooperating with the special counsel Robert Mueller's office's investigation into Russian interference in the 2016 US election and possible collusion with President Donald Trump's campaign.

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In a sentencing memo released on December 11, prosecutors detailed the extent of Flynn's cooperation: thousands of documents, over 62 hours of meetings with officials, and facilitating the procurement of electronic devices. Mueller's office recommended 200 hours of community service and no prison time.

During his sentencing hearing on Tuesday, prosecutors said that further cooperation "remains a possibility."