Prosecutors working for US special counsel Robert Mueller have accused former Trump campaign chairman Paul Manafort of trying to tamper with witnesses in his ongoing criminal cases.

They have asked a US federal judge to consider revoking Manafort’s house arrest.

In a court filing, prosecutors wrote that Manafort and one of his associates repeatedly contacted two witnesses to try to influence their testimony. The contacts occurred earlier this year, shortly after a grand jury returned a new indictment against Manafort and while he was confined to his home.

Court documents do not name Manafort’s associate, but they refer to him as “Person A” and note the pseudonym is consistent with previous filings in the case.

In earlier filings, Person A has referred to Konstantin Kilimnik, a longtime Manafort associate who prosecutors have said has ties to Russian intelligence.

The two witnesses are also not named in court filings. But prosecutors say they worked with Manafort in organising a group of former European officials, known as the Hapsburg Group, who promoted Ukrainian interests in Europe as well as the US.

Paul Manafort’s former business partner, Rick Gates. Photo: AAP

Manafort began messaging and calling one of the witnesses in February, shortly after a federal grand jury in Washington returned a superseding indictment against him that included allegations of unregistered lobbying related to the Hapsburg Group, according to the court filing.

Manafort messaged and called one of the witnesses the day after his co-defendant and business partner, Rick Gates, pleaded guilty and continued reaching out over the next several days, according to a sworn affidavit filed by an FBI agent in the case.

The person told investigators that he interpreted Manafort’s efforts to reach him as a way to influence his potential statements.

Manafort faces several felony charges in two federal cases. He has pleaded not guilty.

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

Trump has denied collusion with Russia and called Mueller’s investigation a “witch hunt.”