WASHINGTON (REUTERS) - A US judge on Thursday (Nov 2) ordered President Donald Trump's former campaign manager Paul Manafort to remain under home arrest and wear an electronic monitoring device for now as he awaits a tentative trial date on money-laundering and other charges.

Manafort, who ran Trump's presidential campaign for several months last year, and his associate Richard Gates pleaded not guilty on Monday (Oct 30) to a 12-count indictment.

The charges include conspiracy to launder money, conspiracy against the United States and failing to register as foreign agents of Ukraine's former pro-Russian government. They are part of Special Counsel Robert Mueller's investigation of alleged Russian efforts to tilt the 2016 election in Trump's favour and into potential collusion by Trump's associates.

The investigation has cast a shadow over the first nine months of the Republican's presidency.

Another top Trump former campaign advisor, Sam Clovis, withdrew his candidacy for an administration job, apparently as a result of Mueller's probe.

For Manafort and Gates, a conviction on conspiracy to launder money alone could carry a sentence of up to 20 years in prison. Both men appeared in court in Washington on Thursday.

US District Judge Amy Berman Jackson said initial bail terms for the pair would remain in place for now, and set a bail hearing for Monday (Nov 6) to consider changes.

Manafort and Gates are under house arrest, under unsecured bonds of US$10 million (S$14 million) and US$5 million respectively, which means they do not have to post the bail unless they fail to show up for court or violate other conditions.

Prosecutors have argued there is a risk the men would flee. They are also subject to electronic monitoring. Manafort's attorney, Kevin Downing, argued that while his client is willing to comply with a daily curfew, he would like to have the GPS monitoring lifted.

Jackson expressed reservations about the idea, saying she would "need to see some good reasons" and that he must articulate those in writing.

"I am concerned - very concerned ... that an unsecured appearance bond in and of itself is not sufficient" without some sort of monitoring, she said. "If they leave and don't come back, we need to know where they went."

In a filing with the court, Downing said the government's case against his client is flimsy and that the bail conditions should be softened because Manafort does not pose a flight risk.

Gates' attorneys made a similar request.

Manafort and Gates remained quiet throughout the proceeding. Jackson set a bail hearing for Monday morning, and said she would aim to set a tentative trial date next week. She sharply warned lawyers for the duo about speaking about their case outside of court.

"This is a criminal trial and not a public relations campaign," Jackson said during a hearing. "I expect counsel to do their talking in the courtroom and in their pleadings, and not on the courthouse steps."

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Mueller's team is probing allegations that Russia interfered in the election to undercut Americans' faith in their democracy, damage Democratic candidate Hillary Clinton and help Trump. The inquiry also is meant to determine whether there was any coordination between Russians and associates of the Trump campaign.

The Kremlin has repeatedly denied meddling. Trump has denied collusion between his associates and Russia, calling the investigations a witch hunt.

Trump had nominated Clovis, his campaign's national co-chairman, to a post as chief scientist at the Department of Agriculture. In a letter to Trump describing his decision to withdraw from consideration, Clovis made no mention of the Russia controversy, but cited "the political climate inside Washington."

"The relentless assaults on you and your team seem to be a blood sport that only increases in intensity each day," Clovis wrote in the letter. "As I am focused on your success and the success of this Administration, I do not want to be a distraction or negative influence."

A source familiar with Mueller's investigation identified Clovis as the unnamed campaign supervisor in a court filing who had discussions with Trump campaign foreign policy adviser George Papadopoulos about efforts to improve US-Russian relations and setting up meetings between senior Trump campaign and Russian officials.

Papadopoulos pleaded guilty earlier this month to lying to Federal Bureau of Investigation agents about his dealings with Russians. Clovis has not been charged with wrongdoing.

"Mr Clovis' nomination was only withdrawn because that would certainly have been a topic during his upcoming testimony, under oath, before the Senate Agriculture Committee," Democratic Senator Patrick Leahy, a member of the committee, said.

"I know because I was going ask him all about it to get more facts on the record and before the American people."