MOSCOW (AP) — Russia's highest court ruled Thursday to free the jailed business partner of former oil tycoon Mikhail Khodorkovsky three months early, but left in place a back tax claim of 17 billion rubles ($500 million) that will in effect prevent Khodorkovsky from returning to Russia.

Khodorkovsky was pardoned in December by President Vladimir Putin and put directly on a plane to Berlin. Now his partner Platon Lebedev is to walk free.

Both men spent more than 10 years in prison in a case seen as revenge for Khodorkovsky challenging Putin's economic and political power in the early years of his presidency.

Khodorkovsky has said he would not return to Russia as long as the back tax claim remained in force, because it could be used to prevent him from leaving the country again.

Since his release, Khodorkovsky has been cautious in any criticism of Putin. He has insisted that he has no interest in getting involved in Russian politics or fighting for the return of his oil company, Yukos, most of which was taken over by state-owned Rosneft.

Instead, Khodorkovsky said his priority would be to win the release of Lebedev and the former Yukos security chief, Alexei Pichugin, who was convicted of murder and sentenced to life in prison.

Khodorkovsky and Lebedev were arrested in 2003 and convicted in 2005 of evading taxes on Yukos. They were convicted again in a second case in 2010 on charges of stealing oil from Yukos and laundering the proceeds.

The Supreme Court ruled Thursday to reduce Lebedev's prison sentence to 10 years, six months and 22 days. Since Lebedev was arrested on July 2, 2003, this means he should be released as early as Friday from a prison in the northwestern Arkhangelsk region.

But the court ruled that there were no grounds to remove the back tax claim against Khodorkovsky and Lebedev, although the Strasbourg-based European Court of Human Rights ruled in July that Russia had charged the huge tax arrears unfairly.

"I got the message," Khodorkovsky said in a telephone interview Thursday with the New Times magazine. "I raised the question publicly and they answered me publicly in their refusal to abide by the European court's decision. This means only one thing: They would not be happy to see me in Russia."

Rights activist Lev Ponomaryov said he understood why the Kremlin has effectively barred Khodorkovsky from Russia. "When he was in prison, Khodorkovsky earned the right to be a moral authority in Russia," Ponomaryov said in an interview with the Interfax news agency. "Apparently there are fears that he would consolidate civil society and the opposition."

At the time of his arrest, Khodorkovsky was Russia's richest man and drew little sympathy from most Russians. But through his political writings from prison, deportment in court and refusal to bend, he won widespread respect.

Putin pardoned Khodorkovsky so he could see his mother, who is ill and receiving medical treatment in Germany.

His release was played as part of a Kremlin campaign to sooth Western criticism of Russia's human rights record ahead of the 2014 Winter Olympics in Sochi. But by freeing Khodorkovsky eight months before the end of his sentence, Putin was able to release his former rival on his own terms and arrange for him to be sent out of the country.