US prosecutors have accused Donald Trump’s former campaign manager, Paul Manafort, of trying to tamper with potential witnesses ahead of his trial.
Robert Mueller, who is investigating alleged Russian election interference, said Mr Manafort had contacted people related to his money laundering and tax fraud case in breach of his bail terms.
Mr Manafort, 69, denies all charges.
They are not connected with allegations of collusion between Russia and the Trump campaign during the US election.
Mr Trump denies any collusion and has consistently spoken of a witch-hunt.
Mr Manafort’s first trial, on charges of money laundering and illegal lobbying, is due to begin in September.
According to Mr Mueller’s motion, Mr Manafort contacted witnesses who would be called to testify about unlawful lobbying allegedly carried out on behalf of Ukraine’s previous pro-Russian government.
Mr Manafort is said to have made tens of millions of dollars from a campaign to bolster that government’s reputation within Europe and the US, but failing to register this work.
The communications with witnesses were an “effort to influence their testimony and to otherwise conceal evidence”, FBI Special Agent Brock Domin wrote in a separate declaration filed to the court.
Mr Manafort resigned as chairman of the Trump campaign in August 2016. He has been under house arrest since he was charged last October.
Mr Mueller urged the judge to review the conditions of his release from jail.
Mr Manafort’s reaction to the new allegations of witness tampering was not immediately known.
His other trial – on tax fraud charges – is due to start next year.
Mr Mueller’s investigation, which began last year, has so far issued 22 indictments: 16 to Russian individuals and companies and the rest to Americans.
The former Trump campaign and administration staff indicted also include Michael Flynn, the president’s former national security adviser; Rick Gates, a former deputy campaign chair; and George Papadopoulos, a former foreign policy adviser.
The three have worked out plea deals with prosecutors and said they are co-operate with the main investigation.