Russian investigators have formally accused the former oil tycoon Mikhail Khodorkovsky of involvement in the murder of a Siberian mayor in 1998.
Mr Khodorkovsky denies he had anything to do with the killing and says the charges are politically motivated.
He says he has no plans to return to Moscow to appear before the investigative committee.
Earlier this week, he said a revolution to end President Vladimir Putin's rule was "inevitable and necessary".
He also warned that the collapse in the value of the rouble could lead to Russia's cash reserves running out within the next two years.
Once Russia's richest man, he now lives in exile in Europe, after spending 10 years in a Russian prison.
The latest accusations relate to the killing of Vladimir Petukhov, the mayor of Nefteyugansk, the town where Khodorkovsky's oil company, Yukos, was headquartered at the time.
Mr Khodorkovsky was jailed for tax evasion and theft after funding political parties opposed to Mr Putin, but was released in 2013 following a presidential pardon from the president.
Timeline: Mikhail Khodorkovsky
1963 - Born in Moscow, son of chemical engineers
1987 - Founds Menatep bank
1995 - Buys Yukos for $350m, with Menatep assuming $2bn in debt
2003 - Arrested for tax evasion, embezzlement and fraud
2005 - Found guilty on six of seven charges, jailed for eight years
2007 - Yukos declared bankrupt
2010 - Convicted of embezzlement and money laundering
2013 - Pardoned by President Putin after a request for clemency; leaves Russia for Germany