FILE PHOTO: Former U.S. National Security Adviser Michael Flynn departs U.S. District Court, where he was expected to plead guilty to lying to the FBI about his contacts with Russia's ambassador to the United States, in Washington, U.S., December 1, 2017. REUTERS/Jonathan Ernst

WASHINGTON (Reuters) - U.S. President Donald Trump’s former national security adviser Michael Flynn, who pleaded guilty to lying to the FBI, will be sentenced on Dec. 18, according to a court filing on Wednesday.

Flynn pleaded guilty in December 2017 to lying to the FBI about his contacts with Russia, in exchange for cooperating with Special Counsel Robert Mueller’s probe into Russian interference in the 2016 presidential election.

A joint filing at U.S. District Court in Washington on Monday by Flynn’s lawyers and prosecutors had said Flynn could be sentenced as soon as Nov. 28.

Prosecutors have repeatedly deferred Flynn’s sentencing date since his guilty plea, even though Flynn’s lawyer Robert Kelner said at a July hearing his client was eager to get the sentencing date on the calendar and put the ordeal behind him.

A sentencing date signals that Flynn’s ongoing cooperation with Mueller’s office is coming to an end.

Flynn was the first member of Trump’s administration to plead guilty to a crime uncovered by Mueller’s wide-ranging investigation into Russian attempts to influence the 2016 U.S. election and potential collusion by Trump aides.

Under a plea bargain deal, Flynn admitted in a Washington court that he lied when asked by FBI investigators about his conversations with Russia’s then-ambassador, Sergei Kislyak, just weeks before Trump took office.

Trump has denied knowing anything about contact with Russians and his campaign and has called Mueller’s probe a witch hunt. Russia has denied U.S. allegations that it interfered in the campaign.