The single-page document, filed at the US District Court for the District of Columbia, did not reveal the nature of the new charges in the case involving former campaign manager Paul Manafort and aide Rick Gates.

Its inclusion in a binder in the court clerk's office that is routinely updated with new criminal charges signals that Mueller's office may have filed a superseding indictment replacing a previous one from last year against the two men.

Manafort, who was Trump's campaign manager for almost five months in 2016, and Gates, who was deputy campaign manager, were indicted by Mueller's office in October.

They face charges including conspiracy to launder money, conspiracy to defraud the United States and failure to file as foreign agents for lobbying work they did on behalf of the pro-Russian Ukrainian Party of Regions.

Both have pleaded not guilty.It was unclear when any new charges would be announced publicly.

Last Friday, Mueller's office revealed in a court filing that it had uncovered "additional criminal conduct" by Manafort in connection with a series of "bank frauds and bank fraud conspiracies" related to a mortgage on his property in Fairfax, Virginia, a Washington suburb.

Mueller is probing Russia's interference in the 2016 US presidential election, whether Trump's campaign colluded with Russia and whether the Republican president has unlawfully sought to obstruct the investigation. Russia denied the allegations. Trump said there was no collusion.

The Special Counsel's office declined to comment on the new court filing. Lawyers for Manafort and Gates could not be immediately reached for comment. A spokesman for Manafort declined to comment.

Last year, US. intelligence agencies found that Russia had meddled in the election and that its goals eventually included aiding Trump who won a surprise victory over Democrat Hillary Clinton.

Australian Associated Press