Donald Trump's former campaign chairman Paul Manafort has breached his plea deal by lying to federal investigators, according to a court filing, in a potential setback to the special counsel's probe into Russia's meddling in the 2016 United States presidential election.
The torpedoing of Manafort's plea deal could expose him to a lengthier prison sentence and potentially more criminal charges.
Mueller, who is also probing possible collusion between Moscow and the Trump campaign, said in the filing that after signing a 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".
By breaching his plea agreement, Manafort will lose the benefit of prosecutors recommending that he receive leniency at his sentencing.
In the status report, which was filed after the parties had asked for a delay in the previous deadline, Manafort denied that he had not been cooperative.
Manafort was convicted on 8 counts in September in the Eastern District of Virginia for failure to register as a foreign agent in light of his political connection to former Ukrainian president Viktor Yanukovych, alongside charges of tax-evasion, conspiracy and lying to federal agents. Before his plea agreement, Manafort aggressively challenged the special counsel's legitimacy in court, went through a bitter trial and landed himself in jail after prosecutors discovered he had attempted to tamper with witnesses in his case.
Instead, he agreed to plead guilty to two charges of conspiracy, and to cooperate with federal investigators as they probe Russian interference in the 2016 election.
"He believes he has provided truthful information and does not agree with the government's characterization or that he has breached the agreement", it says. The agreement avoided a second trial on money laundering and other charges.
Trump has repeatedly denied collusion of any kind.
He faced up to 10 years in prison under the deal and will also forfeit four of his properties and the contents of several bank accounts.
The special counsel's office says it will provide more details at a later date. It is not clear if these charges will now be refiled.
Manafort, 69, was thought to be a star witness in the probe into whether the Trump campaign colluded with Russian Federation, given his knowledge of President Donald Trump's presidential campaign.
Manafort, a longtime Republican political consultant ran the Trump campaign.
Following his conviction, President Trump praised his former campaign chairman for refusing to "break" under legal pressure.