A former Trump campaign adviser should spend at least some time in prison for lying to the FBI during the Russia probe, prosecutors working for special counsel Robert Mueller said in a court filing Friday that also revealed several new details about the early days of the investigation.

The prosecutors disclosed that George Papadopoulos, who served as a foreign policy adviser to U.S. President Donald Trump's campaign during the 2016 presidential campaign, caused irreparable damage to the investigation because he lied repeatedly during a January 2017 interview.

Those lies, they said, resulted in the FBI missing an opportunity to properly question a professor Papadopoulos was in contact with during the campaign who told him that the Russians possessed "dirt" on Hillary Clinton in the form of emails.

The filing is the first public acknowledgement by the special counsel's office that the FBI interviewed professor Joseph Mifsud during the early part of the investigation into Russian election interference and possible co-ordination with Trump associates. The filing doesn't relate the details of the interview but refers to it as a missed opportunity caused by Papadopoulos.

"The defendant's lies undermined investigators' ability to challenge the Professor or potentially detain or arrest him while he was still in the United States," Mueller's team wrote, noting that the professor left the U.S. in February 2017 and has not returned since.

Prosecutors note that they also missed an opportunity to interview others about the professor's comments or anyone else at that time who might have known about Russian efforts to obtain derogatory information on Clinton during the campaign.

"Had the defendant told the FBI the truth when he was interviewed in January 2017, the FBI could have quickly taken numerous investigative steps to help determine, for example, how and where the Professor obtained the information, why the Professor provided the information to the defendant, and what the defendant did with the information after receiving it," according to the court filing.

Prosecutors also detail a series of difficult interviews with Papadopoulos after he was arrested in July 2017, saying he didn't provide "substantial assistance" to the investigation. Papadopoulos later pleaded guilty to lying to the FBI as part of a plea deal.

The filing recommends that Papadopoulos spend at least some time incarcerated and pay a nearly $10,000 US fine. His recommended sentence under federal guidelines is zero to six months, but prosecutors note a similar defendant in the case spent 30 days in jail for lying to the FBI.