MOSCOW – Russia has asked Britain to extradite a former oil tycoon who fled after what he said was severe harassment by the government, an investigative official said Monday.

Mikhail Gutseriyev, the former president of Russneft, fled the country last year amid what he said was “unprecedented hounding” from the state, including a tax-evasion probe. Analysts linked his troubles to a dispute with the state-run oil giant Rosneft over some oil fields.

Gutseriyev is in Britain and Russia has sent documents requesting his extradition, said Igor Tsokolov, spokesman for the Interior Ministry's Investigative Committee.

Russneft was Russia's seventh-largest oil company when Gutseriyev headed it. Pressure on Gutseriyev began to mount late in 2006, when federal prosecutors opened a criminal investigation. Charges of tax evasion and illegal business activity for exceeding production quotas at Russneft were filed against him last year.

Russia has unsuccessfully asked Britain to extradite other prominent figures wanted on what the accused claim are politically motivated charges, including the tycoon and former Kremlin insider Boris Berezovsky and Chechen separatist Akhmed Zakayev.

Relations between Britain and Russia plummeted to a post-Cold War low amid Russia's demands for the extradition of its foes and its refusal to hand over the suspect in the 2006 radiation poisoning death of Alexander Litvinenko, an associate of Berezovsky.

Critics say the Kremlin used groundless criminal charges to strengthen its control over the lucrative oil industry under former President Vladimir Putin, who is now prime minister. Former Yukos oil company chief Mikhail Khodorkovsky is serving an eight-year prison sentence on fraud and tax evasion charges.

Most of Yukos' former assets are now in the hands of Rosneft.