Russian oligarch Oleg Deripaska has filed a lawsuit in a Washington court against the U.S. Treasury Department, alleging the sanctions against him are illegal and claiming they have cost him $7.5 billion.

Deripaska, a powerful tycoon with close ties to the Kremlin, names the Treasury, Treasury Secretary Steven Mnuchin, and Andrea Gacki, who leads the Treasury's sanctions unit, in his suit filed on March 15.

Deripaska claims he has been unfairly swept up in a "general hysteria" because of unfounded allegations spread by members of U.S. Congress and others amid Special Counsel Robert Mueller's investigation into possible collusion between Russia and the presidential campaign of Donald Trump.

A Treasury spokesman declined to comment and referred news agencies to the Justice Department, which also declined to comment.

The Treasury in April 2018 imposed sanctions on three companies linked to Deripaska -- Russian aluminum giant Rusal, its parent company En+, and power firm EuroSibEnergo.

The Treasury’s Office of Foreign Assets Control (OFAC) alleged that Deripaska and other Russian oligarchs were profiting off their links to Russian President Vladimir Putin and from Moscow's "malign activity" around the globe.

But, given Rusal's size and importance, the sanctions roiled global metals markets, unnerving businesses in the United States and Europe.

The U.S. administration later reached a deal with the three Russian firms to end Deripaska's control in return for a lifting of sanctions, forcing the oligarch to divest much of his holdings.

News reports have since documented how Deripaska’s divestments may end up benefiting family members, other oligarchs, and a state-controlled Russian bank.

In his suit, Deripaska claimed the sanctions made him an industry outcast, avoided by business partners and banks, and led to the reduction of his net worth by four-fifths.

"The effect of these unlawful actions has been the wholesale devastation of Deripaska's wealth, reputation, and economic livelihood," his attorney,
Erich Ferrari, wrote in the 28-page lawsuit.

Michael Dobson, a former senior OFAC official who dealt with Russia sanctions before leaving the agency, called the suit an "annoyance claim" that was unlikely to be successful.

"Ultimately I don't really think this case is going to go far," Dobson, who is now with the Morrison & Foerster law firm, told AFP news agency.

With reporting by AFP and AP