MOSCOW - Russian President Vladimir Putin pardoned on Friday Mikhail Khodorkovsky, a former oil tycoon and one of Russia's most famous prisoners.

Oil tycoon Mikhail Khodorkovsky (R) is escorted by a security officer before an appeal hearing against his fraud conviction in Moscow City Court in this September 20, 2005 file photo. [Photo/Agencies]

"Guided by the principal of humanism, I order to grant pardon to Mikhail Khodorkovsky, freeing him from further imprisonment," Putin said in a decree shown on the Kremlin website.

The decree took effect immediately, and Khodorkovsky reportedly left his penal colony around noon in the town of Segezha in northern region of Karelia, near Russia's border with Finland.

The pardon came a day after Putin attended a four-hour annual press conference, when he said the release was based on humanitarian reasons.

Putin noted that Khodorkovsky should have signed necessary document requesting the pardon earlier, "which he didn't do."

"But recently he signed this document, and it was addressed to me with an appeal for clemency," he said, adding the fifty-year-old man had already served a long sentence for a serious crime.

Khodorkovsky, former Yukos CEO, was arrested in 2003. In May 2005, a Moscow district court sentenced him to nine years in prison for fraud and tax evasion. That sentence was later reduced to eight years.

In December 2010, Khodorkovsky was sentenced to 14 years in prison for oil theft and legalization of proceeds from its sale and the sentence was later cut to 13 years. In 2012, Russian Supreme Court revised his prison term to expire in August, 2014.

The former tycoon has repeatedly insisted on his innocence, and that the criminal case against him was politically motivated.