WASHINGTON (Reuters) - President Donald Trump’s former national security adviser Michael Flynn knew better than to lie to the FBI and does not deserve sentencing leniency because he was not warned that lying to federal agents was a crime, U.S. prosecutors said on Friday.

The rebuke by Special Counsel Robert Mueller came after Flynn’s lawyers argued that the lack of an explicit warning before an interview with FBI agents in January 2017 should be a mitigating factor in his sentencing on Tuesday.

“A sitting National Security Adviser, former head of an intelligence agency, retired Lieutenant General, and 33-year veteran of the armed forces knows he should not lie to federal agents,” Mueller’s office said in a court filing.

“He does not need to be warned it is a crime to lie to federal agents to know the importance of telling them the truth.”

Flynn pleaded guilty in December 2017 to lying to the FBI agents about his conversations with Russia’s then-ambassador, Sergei Kislyak, and has been cooperating with Mueller’s probe into Russia’s meddling in the 2016 U.S. election.

The FBI interview took place on Jan. 24, 2017, soon after Trump took office.

In the filing Mueller said Flynn lied to the media and senior administration officials in the weeks leading up to the interview, telling them he had not discussed U.S. sanctions against Russia with Kislyak when in fact he had.

“Thus, by the time of the FBI interview, the defendant was committed to his false story,” Mueller’s prosecutors wrote.

Mueller’s filing was in response to an order by the judge to turn over documents related to the interview.

That order, in turn, followed a sentencing memo earlier this week by Flynn’s lawyers in which they argued for leniency.

As mitigating factors, Flynn’s lawyers cited both the lack of a warning about lying and a suggestion by then-FBI Deputy Director Andrew McCabe to Flynn that the “quickest way” to conduct the interview was without counsel present.

Critics of the Mueller probe had jumped on those assertions to promote the idea that Flynn had been set up.

Flynn’s crime of lying to the FBI carries a statutory maximum sentence of five years in prison. His plea agreement states, however, that he is eligible for a sentence of zero to six months and can ask the court not to impose a fine.

Mueller, who last week cited Flynn’s “substantial” cooepration in recommending no prison time, said in Friday’s filing that Flynn still deserved a sentence at the low end of the federal guideline range providing “the defendant continues to accept responsibility for his actions.”

Trump has denied there was collusion between his presidential campaign and Russia, and has labeled Mueller’s probe a “witch hunt.” Russia has denied it meddled in the election, contrary to the conclusion of U.S. intelligence agencies.