Russian President Vladimir Putin signed a decree on Friday pardoning jailed tycoon Mikhail Khodorkovsky, after he spent a decade in jail, the Kremlin said. A few hours later he left prison, his lawyer reported.

Putin announced unexpectedly on Thursday that he would pardon Khodorkovsky, in what may be a gesture to critics of his human rights record before Russia hosts the Winter Olympics.

The decree pardoned Khodorkovsky on the basis of "the principles of humanism". The Kremlin said the decree took immediate effect and Russian news agencies quoted a lawyer as saying it was possible that the former Yukos oil company chief could be freed as early as Friday.

Khodorkovsky was reportedly en route to Berlin Friday afternoon,a German official reported.

Khodorkovsky, 50,  was once Russia's richest man and is seen by Kremlin critics as a political prisoner. He fell out spectacularly with Putin a decade ago. His company, Yukos, was broken up and sold off, mainly into state hands, following his arrest at gunpoint on an airport runway in Siberia on fraud and tax evasion charges in 2003.

He became a symbol of what investors say is the Kremlin's abuse of the courts for political ends. The Kremlin denies this but Putin has singled Khodorkovsky out for bitter personal attacks and ignored many calls for his release.

On Thursday, however, Putin said: "He has been in jail already more than 10 years. This is a serious punishment."

Saying Khodorkovsky's mother was ill and that he had asked for clemency, he added: "I decided that with these circumstances in mind ... a decree pardoning him will be signed."

Russian shares rose over 1 percent on the news, though later settled back by the end of the day.

A sustained rally would require "a consistent track record of implementation of market-friendly reforms - in particular, of steps to improve the judicial system, so that decisions are more predictable and property rights better protected," a Moscow-based economist at an investment bank said.

Lawyers for Khodorkovsky initially said he had not sought clemency but his representatives later said they were trying to reach him in prison near the Arctic Circle to clarify matters.

An early release had not been expected and there had even been speculation that new charges might be brought against him, as they were before his sentence was extended in 2010 after a second trial for theft and money-laundering.

Khodorkovsky began dabbling in small business as a Moscow student Communist leader under Mikhail Gorbachev's perestroika reforms of the late 1980s. Still in his 30s, he emerged from the cut-throat chaos of the Soviet collapse as one of the wealthiest "oligarchs" under Putin's predecessor Boris Yeltsin.

His fall from grace after criticizing Putin, a former KGB officer, has long been held up by foreign investors as evidence of the weakness of property rights and the rule of law in Russia.