“As far as a third case is concerned, I do not want to go into the details, but as a person who is looking at this from the side, without immersing myself in it, I do not see any special prospects in this sense,” Putin told an annual press conference.

“I do not really understand where there is a case. I heard that people are talking about it, but I do not see any threats there against anyone,” Putin said.

Russian investigators said earlier this month they were probing several more criminal cases against former Yukos oil company chief, who has been in prison since 2003.

Once Russia’s richest man who openly backed parties opposed to Putin’s rule, Khodorkovsky was convicted of fraud and tax evasion in 2005.

A second trial ended in 2010 with an embezzlement conviction, prompting Western governments to accuse the Kremlin of pursuing selective justice.

Although Putin has no formal influence over criminal investigations or the court system, his word carries overwhelming force in Russian politics.

Putin in December 2010 notoriously used a television appearance to declared in reference to Khodorkovsky that a “thief must be in prison.” The tycoon was convicted for the second time later that month.

The 50-year-old is due to be released in August 2014.