Former German Foreign Minister Hans-Dietrich Genscher (R) welcomes Russian former oil tycoon Mikhail Khodorkovsky at Berlin's Schonefeld airport, in this December 20, 2013 handout picture provided by Khodorkovsky website. Khodorkovsky left Russia for Germany after his release from prison on Friday following a presidential pardon, the Russian federal prison service said. [Photo/Agencies]

MOSCOW/BERLIN  - Mikhail Khodorkovsky, the Russian oil tycoon jailed for a decade, was freed by a presidential pardon on Friday and immediately flew to Berlin where he hoped to be reunited with his family.

Once Russia's richest man, the 50-year-old looked pale and thin but happy in a photograph of him being greeted by German well-wishers on the tarmac after landing on a private jet.

President Putin, who surprised Russians and gave a brief lift to the stock market by announcing Khodorkovsky's pardon on Thursday, said he was acting out of "principles of humanity" because Khodorkovsky's mother is ill.

Within hours of being released from Penal Colony No. 7 at Segezha, deep in the sub-Arctic forest near the Finnish border, Khodorkovsky was in the German capital and issued a statement confirming he had sought a pardon and had not admitted guilt.

"I appealed to the Russian president on November 12 with a request for a pardon in connection with family circumstances," he said. "The issue of an admission of guilt was not raised."

Putin's spokesman said the Russian president had received two letters from Khodorkovsky - a long personal letter and the official pardon request. The pardon was granted unconditionally and Khodorkovsky was free to return to Russia, he said.

The former oil baron had been due to be released next August but supporters feared the sentence could be extended, as it was before. He spent the last few years working at the jail, in an area once part of Stalin's Gulag labour camp system.

With a note of defiance, Khodorkvsky thanked wellwishers for their support "to me, my family and all those who were unjustly convicted and continue to be persecuted".

"My father is free and safely in Germany," his son, Pavel Khodorkovsky, said on Twitter. "Thank you all for the support you've given my family over these years!"

His mother Marina, 79, told Reuters from her home outside Moscow: "I want to just hug him. I don't even know yet what I am going to say to him."

Her son said last month that she was facing a second bout of cancer and he might not see her again. His father told Reuters they planned to travel to Berlin on Saturday.

GERMAN ROLE

He was greeted at the airport by Hans-Dietrich Genscher, the former German foreign minister who played a major role in East-West relations at the end of the Cold War and who had helped organise the plane to bring Khodorkovsky to Berlin.

Khodorkovsky had not immediately realised that his mother, who had undergone treatment in Germany, had returned to Russia, Genscher told Der Spiegel online.

Genscher told ARD television Putin had received him twice to talk about Khodorkovsky and Chancellor Angela Merkel said she had "repeatedly urged" the Russian president to free him.

The oil baron's 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.