Moscow ? OAO Yukos, once Russia’ biggest oil company, was declared bankrupt Tuesday after a three-year campaign by government tax authorities that critics called a politically motivated campaign against Yukos’ founder.

The government cast its actions as a crusade against a rotten corporate empire. The campaign rattled Russia’s investment climate, and the bankruptcy declaration opened the way for the Kremlin to further tighten its grip on the strategically vital energy sector.

The ruling was a muted epilogue that followed the conviction of Yukos’ billionaire founder Mikhail Khodorkovsky last summer and the sale of the company’s production unit Yuganskneftegaz to the state after a disputed auction in December 2004.

Some considered the case punishment for Khodorkovsky’s perceived political ambitions. The trials of Yukos officials and multibillion-dollar tax claims against the company have been widely seen as a campaign by President Vladimir Putin’s Kremlin to punish Khodorkovsky’s financial and political clout.