Russian prosecutors have opened a formal criminal investigation into tycoon Boris Berezovsky for planning a forced takeover of power and asked again for Britain to extradite him.
British Foreign Minister Jack Straw this week warned Mr Berezovsky - who has said publicly that President Vladimir Putin should be driven from office - that his residency status in Britain could be reviewed if he continued to advocate a coup.
A spokeswoman for the prosecutor general said a criminal case was opened against Mr Berezovsky on February 16th and that documents for his extradition were sent to Britain yesterday.
Mr Berezovsky (60) helped Mr Putin to power during the last days of Boris Yeltsin's rule but later fell foul of Mr Putin's Kremlin and fled Russia in 2000, becoming a vociferous enemy from his base in London.
Mr Berezovsky rose to riches and power under Mr Yeltsin and gained major stakes in oil, metals, airline and media businesses, which he has since sold.
The tycoon told a Russian radio station in January that he had been planning a forced takeover of power in Russia for over a year. He said such action was justified because Mr Putin's rule was unconstitutional.
Britain annoyed Moscow by granting Mr Berezovsky asylum status in 2003. and British courts have rejected Russian requests for him to be extradited to stand trial on fraud charges.
The tycoon says those charges are politically motivated. But Mr Straw signalled a new, tougher approach on Tuesday when he warned that Mr Berezovsky could be kicked out of Britain.