Federal prosecutors asked a judge on Monday to sentence former Trump campaign chairman Paul Manafort, saying he broke his plea agreement by lying to the FBI and investigators for special counsel Robert Mueller.

Manafort, 69, was convicted of eight counts of tax evasion and bank fraud in August. In September, he agreed to cooperate with Mueller's investigation when he pleaded guilty to two new counts and admitted his guilt to 10 counts outstanding from the earlier trial in Virginia.

On Monday, prosecutors with Mueller's office told the court that "after signing the plea agreement, Manafort committed federal crimes by lying to the Federal Bureau of Investigation and the Special Counsel's Office on a variety of subject matters, which constitute breaches of the agreement."

The two-page document doesn't say what the government believes Manafort lied about. But Mueller's team said it would file a "detailed sentencing submission" detailing what they said were his "crimes and lies," which could be filed unsealed.

Mueller's office made the assertion in a joint status report filed in U.S. District Court in Washington, D.C., along with attorneys for Manafort, who disputed the assertions that he lied or broke the plea deal.

"After signing the plea agreement, Manafort met with the government on numerous occasions and answered the government's questions. Manafort has provided information to the government in an effort to live up to his cooperation obligations," his lawyers said in the documents.

"He believes he has provided truthful information and does not agree with the government’s characterization or that he has breached the agreement," they said.

His lawyers agreed to move ahead with sentencing because of the big "conflict in the parties' positions."

Paul Manafort, shown with his attorney Richard Westling, pleaded guilty before U.S. District Judge Amy Berman Jackson in Washington, D.C., in September. Art Lien

Both cases against Manafort involved his political consulting for the previous Russian-backed government of Ukraine and its former president, Viktor Yanukovych, well before Manafort served briefly as President Donald Trump's campaign chairman. He was convicted of intentionally having dodged U.S. taxes by stashing the millions he was paid in overseas banks.

Under the plea deal, Manafort agreed to forfeit multiple bank accounts and properties — including his apartment in Trump Tower in New York — and to cooperate with investigators by participating in interviews, providing documents and testifying in court.

The two counts to which Manafort pleaded guilty in September carry a maximum sentence of 10 years in jail and six years of supervised release, as well as up to $500,000 in fines.

The plea deal didn't amount to a guilty plea to the 10 outstanding Virginia charges — three counts of failing to file reports of foreign bank and financial accounts and seven counts of bank fraud and bank fraud conspiracy. However, under terms of the deal, prosecutors can use his admission of guilt against him if it is established that he did violate the agreement.

Paul Manafort leaves federal court in Washington, D.C., in February. Drew Angerer / Getty Images file

The consequences could be severe. Because of the reported breach, Mueller's office has no obligation to inform the court about any helpful cooperation he may have provided, which could have lessened his sentence.

Under the plea agreement, Manafort can't appeal the sentences in the Washington or the Virginia cases, and now prosecutors can ask for "an upward departure" in their new sentencing request — meaning they could ask for more jail time than what Manafort pleaded to originally.

Manafort could also face being retried on the 10 counts on which the jury deadlocked in Virginia, because the judge in that case dismissed those charges without prejudice. The fact that Manafort admitted guilt to them could be presented to the jury.

On Sunday, a federal judge ordered George Papadopoulos, another former Trump campaign aide, to report to jail on Monday for lying to federal investigators. Papadapoulos had sought to delay his reporting date because two appeals against Mueller's authority and his appointment are still active in the courts.

Papadapoulos pleaded guilty last year and was sentenced in September to 14 days in jail.

CORRECTION (Nov. 27, 2018, 5:40 a.m. ET): An earlier version of this article misstated the date of Manafort's conviction. It was August 2018, not February.