Russian police on Wednesday raided the Moscow headquarters of British-Russian oil venture TNK-BP, long considered to be a target of Kremlin nationalization plans for the sector, according to dpa. The incursion and seizure of documents was related to an ongoing tax investigation into Sidanco, one of the firm's subsidiaries, news agency Interfax reported a spokesman for the Interior Ministry's investigative committee as stating Wednesday. Oil trader Sidanco exists under the merger in 2003 of British petroleum firm BP and the Alfa Group, a consortium of Russian billionaire investors including Mikhail Friedman and metals magnet Viktor Velksberg. A TNK-BP company representative said the company "was working as usual." TNK-BP declined to comment further beyond saying it was "ready to cooperate with law enforcement bodies." BP's loss of its majority stake in the massive Siberian oil field Kovykta to Russian energy monopoly Gazprom last year prompted analysts to speculate that Russian investors could sell their stake in TNK-BP to a state-controlled energy firm. President Vladimir Putin has made it an unspoken policy that state-owned firms should hold majority control over companies in Russia's key economic sectors.