Sanctions have stopped Russia’s state-controlled oil group Rosneft expanding its trading operations, the company revealed on Tuesday, preventing it from capitalising on one of the main revenue sources tapped by western rivals during the oil price rout . Marcus Cooper, the Geneva-based head of Rosneft’s trading arm, said western sanctions imposed on Russia after it intervened in Ukraine had slowed the company’s plans to expand dealing overseas and starved it of capital needed to finance big trades.