Mikhail Khodorkovsky has been freed from a Russian prison camp after receiving a pardon from President Vladimir Putin.
The former oil tycoon was released within an hour of the Kremlin publishing a decree, which stated: “Guided by humanitarian principles, I decree that Mikhail Borisovich Khodorkovsky… should be pardoned and freed from any further punishment in the form of imprisonment.
“This decree comes into force from the day of its signing.”
Mr Putin surprised journalists at the end of his annual end-of-year news conference on Thursday by announcing that he was planning to pardon Mr Khodorkovsky.
The 50-year-old former Yukos oil tycoon has been in prison since 2003 after being convicted in two trials on charges including fraud and embezzlement.
Human rights groups criticised both trials and have said they considered Mr Khodorkovsky a political prisoner.
The circumstances surrounding the pardon remained unclear.
Mr Khodorkovsky, once the richest man in Russia, previously said he would not request one because he would be seen to be admitting guilt.
However, the newspaper Kommersant reported that he changed his mind after a meeting with Russian security services, who raised the possibility of a third trial and warned him that his mother’s health was deteriorating.
“This conversation, which was conducted without lawyers, forced Mr Khodorkovsky to turn to the president,” the article said.
Mr Khodorkovsky gained considerable political influence under President Boris Yeltsin in the 1990s as one of the so-called “oligarchs” who surrounded the ailing leader.
However, when Mr Putin became president in 2000, their influence quickly faded.
Economic and political analysts said the announcement was an attempt by Russia to improve its human rights record and international image ahead of the Winter Olympics in February.
Meanwhile, a Kremlin-backed bill is set to end the ordeal of a group of Greenpeace activists who were arrested near an Arctic oil rig in September, and allow two Pussy Riot protesters to be freed.
The amnesty laws would allow investigators to drop charges against the 30 activists, including six Britons who have not been allowed to return home.
Protesters Nadezhda Tolokonnikova and Maria Alyokhina, who were jailed for two years after a demonstration in a Moscow cathedral, would be released early.