In March, police raided BP's Moscow office and its TNK-BP joint venture, which employs 100,000 staff in Russia working on Siberian oil projects.
BP confirmed the latest investigation and said that it was co-operating with the authorities.
Foreign energy companies have come under increasing pressure in Russia as the government has been trying to increase its control over oil and gas assets.
TNK-BP was told last year that it was in danger of losing its production licence for a Siberian gas field for not meeting production targets.
Also last year Royal Dutch Shell was forced to hand over part of its stake in a massive Siberian gas field.




