Russia's third-largest crude oil producer, TNK-BP, has announced that Mikhail Fridman is resigning as the company's chief executive and chairman of the board.
In a statement, the company gave no reason for why Fridman is leaving.
Fridman, 48, was earlier this year ranked by "Forbes" magazine as being in the top 60 of the world's richest people, with a worth of more than $13 billion.
TNK-BP said that in Fridman's place, the company will be managed by a group of executives who hold powers of attorney "related to their areas of responsibility."
Fridman's resignation is due to take effect in 30 days.
Control of TNK-BP, which controls huge oil fields in Siberia, elsewhere in Russia, and Ukraine, is equally split between Russia's Alfa-Access-Renova consortium and British Petroleum.
Based on reporting by Reuters and AFP