WASHINGTON (AP) -- Former Trump campaign chairman Paul Manafort may face additional charges after lawyers in the special counsel's Russia investigation said he lied to them and broke his plea agreement, prosecutors said Friday.

The latest development in Manafort's case comes at a time of public activity in special counsel Robert Mueller's investigation. Prosecutors obtained a guilty plea from President Donald Trump's longtime legal fixer on Thursday and appear to be lining up charges against another Trump supporter.

The prospect of new charges adds to the legal peril of Manafort, the onetime political consultant who already faces years in prison after being convicted of financial fraud crimes in Virginia and pleading guilty to conspiracy counts in Washington.

U.S. District Judge Amy Berman Jackson set a tentative sentencing date of March 5 as prosecutors plan to disclose next week what they believe are the lies Manafort told since pleading guilty in September and agreeing to cooperate with the investigation.

Manafort's lawyers, who deny that Manafort lied, will have an opportunity to respond and a judge is expected to hear arguments before deciding whether he breached his plea deal.

Prosecutor Andrew Weissmann told the judge that prosecutors had not yet decided whether to file new charges against Manafort for the alleged lies, saying, "That determination has not been made."

Trump is facing continued questions about whether he might pardon Manafort. At the same time, he is playing down the significance of the guilty plea of his former lawyer, Michael Cohen, for lying to Congress.

None of the recent moves by Mueller has definitively answered the question of whether Trump or his associates coordinated with Russian interference in the 2016 presidential campaign. And they don't directly accuse the president of any criminal wrongdoing or indicate that the president faces legal jeopardy.

But Trump has continually surfaced in Mueller's investigation, with references to him in Cohen's plea on Thursday and in a draft plea offer extended to conservative writer and conspiracy theorist Jerome Corsi and made public this week.

Trump has expressed sympathy for Manafort, Corsi and his longtime confidant Roger Stone, telling The New York Post this week that they were "very brave" for resisting the Mueller investigation. He said a pardon for Manafort, who has denied lying to investigators, wasn't "off the table."

That prospect of a pardon has drawn criticism, including from Mark Warner, the top Democrat on the Senate intelligence committee who said it would be a "complete abuse of power" and could prompt congressional action against the president.

Manafort faces up to five years in prison on each charge in his plea agreement. He is also set to be sentenced on eight felony counts in a separate case in Virginia in February.

Trump has spent recent weeks casting Mueller's team as hell-bent on destroying the lives of those in the president's orbit. Armed with information passed along by Manafort's attorneys to the president's legal team, Trump has accused prosecutors of dirty tactics and pressuring witnesses to lie.

Trump's lawyers' arrangement with Manafort's lawyers was unusual because it continued after he pleaded guilty to two felony charges and agreed to cooperate with the prosecutors. Trump's legal team also has received help from Corsi. He told The Associated Press that while in contact with Mueller's team, he directed his lawyer to informally share information with Trump's attorneys, including Jay Sekulow.

Sekulow also received the draft plea documents a couple of weeks ago. The legal team alerted the Justice Department but privately was put off by a reference to Trump in the document.

Corsi, who rejected the plea deal, has said he expects to be charged by Mueller with lying to investigators as part of the probe's scrutiny of WikiLeaks and whether he or Stone had advance knowledge of the group's release of thousands of hacked emails stolen from Clinton campaign chairman John Podesta. Mueller and U.S. intelligence agencies have said Russia was the source of the material provided to WikiLeaks.

Both Corsi and Stone have denied having any contact with WikiLeaks or having any foreknowledge of its plans. Corsi also denies making false statements to investigators.