(CNN) The special counsel's office has accused former Trump campaign chairman Paul Manafort of attempting to get witnesses to lie for him in court, and they've asked the judge to send him to jail as he awaits his trial, according to a filing in DC District Court Monday night.

One of the witnesses told investigators recently that Manafort wanted them to commit perjury about a lobbying effort they worked on for him in the US, the filing said.

Manafort is currently out on house arrest and a $10 million unsecured bail. He awaits a trial in Virginia that is scheduled for late July and a trial in DC scheduled to begin in September. He has pleaded not guilty to charges related to his failure to disclose his US lobbying work for a foreign government and to bank fraud and other financial crimes.

Tampering with a witness is a crime in itself -- and it's one Manafort has not yet been charged with.

The new allegation places even more pressure on Manafort, who has stared down prosecutors as they heaped charges on him and say they continue to investigate the possibility that he coordinated with Russians during the 2016 presidential election.

Read More