Gennady Timchenko, a Russian electrical engineer who became an oil-trading billionaire and confidant of President Vladimir Putin, is the focus of a money laundering probe by U.S. prosecutors, two people familiar with the matter said.

Timchenko, 61, who worked for a state oil exporter in the last years of the Soviet Union, helped build Gunvor Group Ltd. into one of the world's largest oil traders in the late 1990s and 2000s. The company got its start selling Russian crude and fuel, including production from state-controlled Rosneft.

The U.S. Attorney's Office in Brooklyn is investigating whether Timchenko sought to launder tainted funds through the U.S. financial system, said one of the people, both of whom requested anonymity because they aren't authorized to speak publicly about the probe. Castor Americas Inc., a U.S. unit of Gunvor, was served with subpoenas by U.S. prosecutors three years ago.