U.S. prosecutors are investigating allegations of money laundering against a member of Russian President Vladimir Putin's inner circle of billionaire supporters, according to a report from the Wall Street Journal

According to the newspaper, prosecutors are investigating whether oligarch Gennady Timchenko transferred funds linked to allegedly corrupt deals in Russia through the U.S. financial system.

At issue are transactions in which Gunvor Group, the international trading company that Timchenko founded, purchased oil from a company that is majority-controlled by the Russian state, and later sold it to third parties. Financial transfers could constitute money laundering if the funds were discovered to have derived from illegal activities, according to the Journal.

The investigation represents the latest front in U.S. authorities' campaign against key Russian and Ukrainian figures, stemming from Russia's intervention in Ukraine. Any U.S. assets that belong to prescribed individuals can be seized, and Russian institutions have been denied access to sectors of the international financial system.

The EU has also placed sanctions on a number of wealthy individuals and companies close to Putin, but Timchenko is not among them.

In August, Timchenko announced that U.S. sanctions were preventing him from using his private jet, after U.S. firm Gulfstream withdrew technical support for the aircraft, as a result of U.S. sanctions, according to a report from the Moscow Times

In early October, Russia's parliament, or Duma, progressed the passage of a law that would allow foreign-owned assets to be seized and used to compensate citizens and companies that have been targeted by Western Sanctions over the war in Ukraine. 

The so-called “Rotenberg Law” is named after Arkady Rotenberg, a wealthy industrialist and close ally of Putin who had $40 million of real estate in Italy seized under EU sanctions.

Timchenko sold his stake in Guvnor to a partner the day before U.S. sanctions against him came into effect. Since then, the Geneva-based company has been seeking to limit its exposure to Russia, which has long been one of the main generators of its profits, according to a Reuters report

U.S. and EU sanctions on Russia have threatened to tip the country's economy into recession. Increasing the pain being caused by international sanctions, the price of oil, a key revenue generator for Russia, is at a 27-month low, according to Bloomberg.

Further compounding Russia's woes, the rouble hit an all-time low on Wednesday after the country's central bank said it would dial back its support for the struggling currency in international markets, according to the Associated Press

In addition, the U.S. and Germany warned Russia Wednesday that it risked further sanctions over the conflict in Ukraine, as the two-month-old truce in the country appeared to be close to unraveling, with fighting erupting in eastern areas of the country, according to Bloomberg