Paul Manafort has until Friday to respond to allegations of witness tampering

A federal judge will decide whether to jail former Donald Trump campaign chairman Paul Manafort while he awaits trial after prosecutors accused him of making several attempts to tamper with witnesses in his criminal case. 

U.S. District Judge Amy Berman Jackson on Tuesday set a hearing for next week and gave Manafort until Friday to respond to the allegations made by special counsel Robert Mueller's team that Manafort and one of his associates "repeatedly" contacted two witnesses in an effort to influence their testimony.

In a statement, Manafort spokesperson Jason Maloni said, "Mr. Manafort is innocent, and nothing about this latest allegation changes our defence. We will do our talking in court."

Manafort has been under house arrest since he was indicted by Mueller in October.

Mueller's team said in a new court filing on Monday that Manafort and one of his associates have "repeatedly" contacted two witnesses — via phone, text message and encrypted messages — in an effort to get them to lie about the nature of lobbying and public relations work they carried out at Manafort's direction on behalf of Ukraine.

Mueller, who is investigating possible collusion between the Trump campaign and Russia, asked the judge overseeing the case in U.S. District Court for the District of Columbia to revoke or revise an order releasing Manafort ahead of his trial.

The two witnesses are not named in court filings, but prosecutors say they are connected to the Hapsburg Group, a firm Manafort worked with to promote the interests of Ukraine. 

The FBI has documents and statements from the two people, as well as telephone records and documents recovered through a search of Manafort's iCloud account, showing the attempted communication, according to FBI Special Agent Brock Domin, in a declaration filed with Mueller's motion. 

"The investigation into this matter is ongoing," Domin wrote.

Manafort is the most senior member of Trump's campaign to be indicted, though the charges do not relate to his campaign activities.

Together with his longtime associate Rick Gates, he is facing two separate indictments on an array of charges in federal courts in Virginia and Washington, D.C.

In the latter he is charged with conspiracy to launder money, conspiracy against the United States, making false statements, and charges in connection with failing to register as a foreign agent, despite lobbying in the United States for the pro-Kremlin Ukrainian government of former president Viktor Yanukovych.

The charges he faces in Virginia include bank fraud and filing false tax returns. 

He has pleaded not guilty to all charges. 

Mueller has recently been dialing up the legal pressure on Manafort, who has opted not to co-operate with investigators.