A lawyer representing Paul Manafort blasted federal prosecutors on Monday for indicting the former Trump campaign chairman on "ridiculous" charges, including money laundering and conspiracy against the United States.

"Today you seen an indictment brought by an office of special counsel that is using a very novel theory to prosecute Mr. Manafort involving a FARA filing," Kevin Downing, a Washington-based attorney who specializes in white-collar crime, told reporters following Manafort's arraignment.

The veteran lobbyist, who was installed at the helm of Trump's campaign in May 2016, was indicted by a federal grand jury on Monday on 12 charges along with his longtime associate Rick Gates.

"Mr. Manafort represented pro-European Union campaigns for the Ukrainians. He was seeking to further democracy and to help the United States," Downing said, referring to Manafort's extensive work for pro-Russia clients.

Downing said the charge of money laundering against Manafort and Gates, who allegedly moved more than $75 million through offshore accounts, is "most ridiculous."

Downing also said federal investigators proved Monday "there is no evidence that Mr. Manafort and the Trump campaign colluded with the Russian government."

Manafort pleaded not guilty to all 12 counts during a hearing at a federal courthouse Monday. He was forced to surrender his passport and will remain under house arrest.