A member of Russian President Vladimir Putin's inner circle and one of the businessmen hit with U.S. sanctions over Russia's actions in Ukraine is under investigation by the U.S. government for money laundering.

Gennady Timchenko, who Forbes says is worth $13 billion, sold his stake in the energy trading company he co-founded a day before the American government slapped sanctions on him in March. Now, reports the Wall Street Journal,  U.S. prosecutors are looking into whether Timchenko funneled money from corrupt business deals in Russia through the U.S. financial pipeline.

The deals in question happened before the sanctions took effect. But Timchenko's former company, Gunvor Group, is alleged to have purchased oil from OAO Rosneft, an oil company owned by the Russian government, at a discoun before selling it off to other companies.

U.S. investigators are now looking into whether Timchenko transferred funds from those transactions — which might have been illegal — through the U.S.

A 2010 story in The Telegraph cited secret U.S. intelligence cables that said Putin was a part owner of Gunvor Group and that a large portion of his wealth has come from the Swiss-based company.

Gunvor Group denied the accusations,saying it had not bought oil from OAO Rosneft in more than two years.

Timchenko has known Putin since the 1990s when Putin was a local official. They still belong to the same judo club in St. Petersburg they joined at the time.

After Putin began his term as Russian president in 2000, Timchenko grew more wealthy, according to the Journal. Between 2002 and 2008, Guvnor — under the guidance of Timchenko — increased the amount of Russian crude oil it shipped by 16 fold.

When Russia invaded Crimea, the strategically located Ukraine peninsula that juts out into the Black Sea, earlier this year, the American government slapped sanctions on several high-ranking and powerful Russian businessmen with ties to Putin and the Kremlin. The sanctions included the freezing of U.S. assets. Similar sanctions at the hands of the European Union placed travel bans on some officials.

In August, Timchenko said his Gulfstream private jet was grounded because U.S.-based Gulfstream Aerospace stopped providing technical support.

"Sanctions are coming out in the quaintest of ways," Timchenko said. "The company Gulfstream has stopped fulfilling its contract obligations by suspending my jet flights."

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