Russian former oil magnate Mikhail Khodorkovsky left prison Friday after being pardoned by President Vladimir Putin, the Federal Penitentiary Service said.

The ex-chief executive of Yukos Oil, regarded by rights activists as Russia's most prominent political prisoner, had spent the past 10 years behind bars after being convicted of tax evasion and embezzlement and receiving a nearly 14-year sentence.

The nation's human rights ombud, Vladimir Lukin, said Khodorkovsky's release would have a positive impact on Russian society.

"This (decision) will have an invigorating and humanizing effect on our society. Our society is sick with fear, hate, excessive suspicion of each other and so on and so forth," Lukin told the Interfax news agency on Friday.

"Such measures as this one are a remedy. We shall see how effective it is. But there is no doubt this is a remedy," the ombudsman said.

Putin announced the decision to pardon Khodorkovsky on Thursday. The former oil tycoon had been due to be released in October 2014, although prosecutors were reportedly pursuing further charges against him.

The president said the man considered by many to be the Kremlin's biggest critic had personally requested the pardon on humanitarian grounds to be able to spend time with his sick mother in Germany.

Russia's erstwhile wealthiest individual, who has been held at a penal colony in a northern region bordering Finland since 2011, had until now refused to request a pardon on principle, saying he was innocent of the charges and such a petition would amount to an admission of guilt.

Shortly after the pardon was announced, Kremlin press secretary Dmitri Peskov said that in submitting the request for clemency Khodorkovsky had acknowledged he was guilty of the charges on which he was sentenced.

Khodorkovsky's release is seen as a bid by Moscow to boost Russia's image before the city of Sochi hosts the Winter Olympics from Feb. 6 to Feb. 23.

The pardon comes just days after Russia's parliament approved an amnesty that lawyers said would free two imprisoned members of punk protest band Pussy Riot, as well as 30 people arrested for a rig-scaling Greenpeace protest against oil drilling in the Arctic.