In federal court documents filed this week, the Department of Justice describes Dmytro Firtash, a former business associate of ex-Trump campaign manager Paul Manafort, as an "upper echelon (associate) of Russian organized crime."

The reference appears in a 155-page filing in federal court in Chicago in response to a motion by Firtash and another defendant, Andras Knopp, to dismiss an indictment against the pair for allegedly trying to set up an international titanium racket.

The court filing is also linked to federal efforts to win Firtash's extradition from Vienna. He was arrested in 2014 at the request of the U.S. and was freed on a $174 million bond.

While purported ties between Firtash and Russian organized crime have been raised in the past, the court filing on Tuesday were the most explicit and public yet by the Justice Department.

The documents filed Tuesday allege that Firtash and Knopp sought "to introduce millions of pounds of illegally obtained goods into the United States" in an alleged scheme involving bribing public officials in India to obtain titanium.

The court filing says the prosecution in the case seeks to target "an effort by a criminal enterprise to infiltrate the United States Commercial sector."

"Moreover," the document says, "Firtash and Knopp have been identified by United States law enforcement as two upper-echelon associates of Russian organized crime."

The documents add, "this prosecution also takes aim at the corruption of foreign public officials, a concern that the Congress has identified as a threat to global security."

The Ukrainian billionaire was an important political and financial player in the pro-Russian political party known as the Party of Regions for which Manafort worked, NBC news reports, quoting a federal complaint and a leaked State Department cable.

At one point, Firtash was involved in a failed effort with Manafort in 2008 to purchase New York's Drake Hotel, NBC News reports, quoting court records.

Manafort resigned as manager of the Trump campaign in August 2016 after his involvement in Ukrainian business and politics came under scrutiny. He later registered with the Justice Department as a foreign agent.

In interviews and statements to NBC News in 2016, Manafort said he “never had a business relationship” with Firtash. “There was one occasion where an opportunity was explored. ... Nothing transpired and no business relationship was ever implemented.”

The effort by Firtash to quash the indictment and the extradition request is shaping up into a major legal battle.

Firtash is represented Lanny Davis, the former White House counsel under President Clinton, Michael Chertoff, former Homeland Security Secretary under President George W. Bush, and former U.S. Attorney Dan Webb, according to the Chicago Tribune.