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WASHINGTON — The Justice Department, in a reversal of its original position, said Tuesday it no longer supports a lenient sentence for Michael Flynn, President Donald Trump's former national security adviser.

Flynn should be sentenced for up to six months, in line with federal guidelines, prosecutors said in a new court filing, instead of probation as they had originally proposed.

Flynn pleaded guilty two years ago to lying about his conversations with Russia’s ambassador to the U.S. during the Trump transition. A year ago, the government said Flynn deserved credit for admitting his misconduct and for cooperating with prosecutors in investigating his former business partner.

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But prosecutors now say he stopped admitting that he had lied to the FBI. And they say he tried to undermine the prosecution of Bijan Rafiekian, his former partner in a lobbying effort on behalf of the government of Turkey. Flynn at first helped the prosecutors bring the Rafiekian case, they said in Tuesday's court filing, but added that "he ultimately hindered their prosecution of it" by backing away from statements he initially made to a grand jury.

Rafiekian was convicted by a federal jury of failing to disclose work on behalf of a foreign government, but a judge later threw out the conviction, concluding that without a clear picture of Flynn's involvement, the evidence was insufficient.

Flynn himself asked for a delay in his sentencing at a hearing a year ago, to give him more time to cooperate with the government. He no longer deserves any credit for any such cooperation, prosecutors said in their court filing.

Flynn pleaded guilty in December 2017 to the charge of lying to the FBI, admitting that he had falsely described the nature of his conversations with the Russian ambassador at the time, Sergey Kislyak, and saying that he accepted responsibility for his actions. But now, prosecutors say, he no longer deserved credit for that, either.

"Far from accepting the responsibility of his unlawful actions, he has sought to blame almost every other person and entity involved in this case, including his former counsel," they wrote.

In recent court filings, Flynn's lawyers described him as "an innocent man" and said the FBI had conducted an ambush-style interview to trap him into making false statements.

Federal District Court Judge Emmet Sullivan last month rejected their claims of prosecutorial misconduct.

Sullivan scheduled sentencing for Jan. 28.