Special Counsel Robert Mueller is seeking to revoke the bail of President Donald Trump's former campaign chairman, Paul Manafort, for allegedly tampering with witnesses in the year-long probe into Russian meddling in the 2016 election, according to a court filing Monday night.

Mueller's team claims Manafort has been engaged in a witness tampering, and therefore violated the conditions of his release.

Mr. Manafort was released to home confinement after his arraignment in October. According to the declaration, Manafort used "an encrypted application" to contact one of the public relations workers a Business Insider article describing the activities of the "Hapsburg Group".

The two witnesses are also not named in court filings.

Manafort has pleaded not guilty.

In one call, the agent wrote, Manafort said he wanted to give the person a "heads-up about Hapsburg".

One minute after sending the news article, Manafort wrote: "We should talk". But prosecutors say they worked with Manafort in organizing a group of former European officials, known as the Hapsburg Group, who promoted Ukrainian interests in Europe as well as the U.S.

The special counsel's office hit Manafort with a 12-count indictment previous year, which included conspiracy against the United States, tax fraud, and money laundering.

Manafort faces multiple felony charges in two federal cases, including conspiracy against the United States, conspiracy to launder money, failing to register as an agent of a foreign principal, giving false and misleading Foreign Agents Registration Act statements and providing other false statements.

The cases are U.S. v. Manafort, 17-cr-201, U.S. District Court, District of Columbia (Washington) and U.S. v. Manafort, 18-cr-83, U.S. District Court, Eastern District of Virginia (Alexandria).