US prosecutors have accused Donald Trump‘s former campaign chairman Paul Manafort, who is facing multiple charges of money laundering, bank fraud and illegal lobbying, of attempting to tamper with witnesses.

A motion submitted by special counsel Robert Mueller on Monday, who is heading up the main investigation into alleged Russian election meddling, said that Manafort had contacted witnesses by phone and encrypted text messaging for the purpose of securing “materially false testimony”.

It added that such activities amounted to a violation of his bail terms, which “triggers the statutory presumption in favour of detention”, meaning he could face jail time before his trials.

Manafort has been under home confinement since he was indicted in October.

According to the court document, he had sought to suborn perjury from witnesses who would be called to testify regarding the activities of the so-called “Hapsburg group” which allegedly carried out unlawful lobbying for Ukraine.

The two witnesses were also not named in court filings, but prosecutors say they were principals in a public relations firm that worked with Manafort in organising Hapsburg group, which includes former European officials.

The group’s work factors into an indictment against Manafort that accuses him of acting as an unregistered foreign agent by lobbying in the US on behalf of Ukrainian interests.

Prosecutors say Manafort directed the group’s work and secretly funnelled more than $2m to it to take positions favourable to Ukraine, including by lobbying in the US without disclosing that they were being paid to favourably represent the country.

Several members of the Hapsburg group have previously denied the allegations.

In February, the 69-year-old pleaded not guilty to charges of money laundering, illegal lobbying and lying, setting up the first trial to result from Mueller’s investigation, due to begin on September 17.

In March, he pleaded not guilty to charges of bank and tax fraud, setting up a separate trial for July 10.

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Monday’s filing marks the second time that Mueller’s team has accused Manafort of violating a judge’s order in the case. Late last year, federal agents discovered that Manafort was attempting to ghostwrite an opinion piece on Ukraine even though he was under a gag order in the case.

Al Jazeera’s Mike Hanna, reporting from Washington, DC, said the fact that lawyers from Mueller’s team brought the urgent motion could point to further developments in the wider probe.

“It is a different team that’s been investing Manafort on various financial charges,” Hanna said.

“But the fact that Mueller’s lawyers have brought this urgent motion could indicate that one of the witnesses involved in this particular document could be linked to the wider probe into Russian collusion that Trump has described as a witch-hunt.”

Manafort spokesman Jason Maloni said his client and his attorneys were reviewing the filing, the Associated Press news agency reported on Monday evening.

22 indictments

Mueller’s investigation has now entered its second year and continues to dominate US politics while menacing Trump’s presidency.

So far the investigation has issued 22 indictments– of which 16 were for Russian individuals and companies associated with online meddling in the 2016 election.

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The remaining include Michael Flynn, Trump’s former national security adviser, who admitted guilt to one count of lying to investigators on December 1; Manafort’s longtime partner and deputy campaign chair Rick Gates and campaign foreign policy adviser George Papadopoulos.

All three worked out plea deals and have pledged to cooperate with the investigation.

Earlier Monday, Trump downplayed Manafort’s role in his election campaign and said the FBI should have informed him that his chairman was under investigation.

“As only one of two people left who could become President, why wouldn’t the FBI or Department of ‘Justice’ have told me that they were secretly investigating Paul Manafort,” he asked on Twitter.

“Paul Manafort came into the campaign very late and was with us for a short period of time [he represented Ronald Reagan, Bob Dole & many others over the years], but we should have been told that Comey and the boys were doing a number on him, and he wouldn’t have been hired!” he also tweeted.