Russian law enforcement officers have raided the Moscow offices of companies belonging to Sibir Energy, the Aim-listed oil group, as the pressure rose on Chalva Tchigirinsky, its main shareholder.

Sibir said that Interior Ministry investigators on Wednesday entered the offices of Magma oil company, a subsidiary of Sibir, and were searching for documents related to the activities of Moscow Oil and Gas Company in 2006 and the Moscow Oil Company in 2002 and 2003. At the time these companies were run by Mr Tchigirinsky.