Exiled former oil tycoon Mikhail Khodorkovsky has said that a new Russian revolution is "inevitable and necessary," and predicted President Vladimir Putin's government will be out of power within a few years.
Speaking on December 9 from London, Khodorkovsky also rejected accusations from Russian authorities of involvement in the killing of a Siberian city mayor in 1998.
Khodorkovsky's remarks at an online news conference were some of his strongest criticism of Putin since he was pardoned by the Russian president in 2013 and flown out of Russia after more than 10 years in prison.
"With the absence of fair elections and other mechanisms for a legal change of power, the only way to change things is revolution," Khodorkovsky said.
Citing an ongoing crackdown on democratic institutions and political dissent, Khodorkovsky suggested Putin had hijacked the country in a "full-fledged unconstitutional coup."
"The return to a legal space is called revolution," he said. "Revolution is inevitable and necessary."
Khodorkovsky, who is 52 and now lives in Europe with his family, said he was not interested in a political career but that he "cannot stand idle and watch what is going on in Russia."
He said that "Putin and his inner circle must be held accountable for what they have done before an independent court. This is my goal."
"Revolution is a good word. It can be and must be peaceful. To make the revolution peaceful is our common goal," Khodorkovsky said.
Kremlin 'Buys Loyalty'
Once Russia's richest man, Khodorkovsky was arrested in 2003 and convicted of financial crimes in trials supporters said were engineered to punish him for challenging Putin and place the assets of his oil company, Yukos, in the hands of the state.
His December 2013 pardon and release is widely seen as part of an effort by Putin to improve Russia's image ahead of the Winter Olympics in Sochi in February 2014.
Russia annexed Crimea the following month and has supported separatists in a conflict that has killed more than 9,000 people in eastern Ukraine since April 2014, leading the United States, European Union, and other Western countries to impose sanctions on Moscow.
Khodorkovsky said that Putin's government had brought Russia into international isolation.
The Kremlin was using the state budget "to buy loyalty" and while trying to pressure the West to lift sanctions, he said.
Khodorkovsky asserted that the Russian government had enough financial reserves to sustain the country's economic situation for only two more years.
"If the West lifts the sanctions, then Russia' current leadership will probably be able to survive for another two years after 2017," he added.
He said Russia's future presidents should not be allowed to serve more than two terms and should be prevented from any attempt to prolong their power.
Putin moved to the prime minister's post in 2008 to avoid violating a bar on more than two consecutive terms, but was elected president again in 2012 and has not ruled out seeking a fourth term in 2018.
Khodorkovsky, who has not returned to Russia since his release but has worked to support its beleaguered liberal opposition parties and movements from abroad, spoke days after Russian investigators summoned him to Moscow for questioning. His spokeswoman said he will not go.
The former oil tycoon told the online news conference that he learned on December 8 that the federal Investigative Committee intends to charge him with involvement into the 1998 killing of Vladimir Petukhov, the mayor of Nefteyugansk, a Siberian city that was the focus of Yukos's main production assets.
Khodorkovsky dismissed the allegations and said they were politically motivated. He said Russian authorities had "falsely linked" Petukhov's killing to Yukos in 2003 after Khodorkovsky publicly spoke about corruption among Russia's top officials, "which irritated Putin."
Former Yukos security chief Aleksei Pichugin is currently serving a life sentence after being convicted of organizing Petukhov's killing and other murders. He and his supporters insist he is innocent.
Putin has suggested in the past that he believes Khodorkovsky had Petukhov killed.
The Investigative Committee announced in June that it had obtained new evidence allowing it to reopen a probe into Petukhov's slaying, with spokesman Vladimir Markin saying Khodorkovsky "might have personally ordered this murder and a number of other extremely serious crimes."
With reporting by AP