WASHINGTON (AFP) - President Donald Trump's former campaign chairman Paul Manafort has violated his plea agreement by lying to investigators, prosecutors said in a court filing on Monday (Nov 26).

Manafort had agreed to cooperate with special counsel Robert Mueller's investigation of possible collusion between the Trump campaign and Russia as part of a plea deal in September.

"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," prosecutors said in the court filing.

In the same joint status report, Manafort's legal team pushed back against the government's assertion.

"Manafort has provided information to the government in an effort to live up to his cooperation obligations," it said. "He believes he has provided truthful information and does not agree with the government's characterisation or that he has breached the agreement."

Manafort agreed to plead guilty to one count of conspiracy against the United States and another count of obstruction of justice in a deal to avert a second trial on money laundering and illegal lobbying charges.

Manafort, who worked for the Trump campaign for nearly six months in the middle of 2016, was already convicted in August on eight counts related to financial fraud during a separate jury trial.

But those charges, as well as the counts covered in the plea deal, were unrelated to the campaign.

Instead, they derived from his work for former Ukrainian president Viktor Yanukovych and his pro-Moscow political party between about 2005 and 2014.