Russian prosecutors have seized a controlling interest in the huge Russian oil company Yukos, after arresting the firm's chief executive last week.

Yukos spokesman Alexander Shadrin says prosecutors seized more than 50 percent of the company's shares in a move he called, illegal.

Mr. Shadrin told Russia's Interfax news agency that Yukos lawyers consider the seizure a gross violation of the Russian criminal code and constitution. He says the shares are owned by foreign investors, who do not have any connection to Yukos chief Mikhail Khodorkovsky.

The prosecutor's office says that Mr. Khodorkovsky controlled the shares.

Russian secret police arrested and jailed Mr. Khodorkovsky last week on seven charges of tax evasion and fraud. At least two other senior Yukos officials are under investigation, and Russian prosecutors have launched a wave of raids on Yukos-affiliated companies during the past four months.

Slumping shares in Russia's largest oil company fell another five percent on word of the seizure.