MOSCOW — President Vladimir Putin is to pardon one of his best known opponents, jailed oil tycoon Mikhail Khodorkovsky, in what may be a gesture to critics of his human rights record before Russia hosts the Winter Olympics.

Putin made the announcement that he would soon free Khodorkovsky, once Russia's richest man, after a marathon news conference in which he exuded confidence that he has reasserted his authority in the face of street protests.

Khodorkovsky, 50, spectacularly fell out with Putin a decade ago and had his Yukos oil company dissolved following his arrest on fraud and tax evasion charges in 2003.

He became Putin's nemesis, a symbol of what investors say is the Kremlin's abuse of the courts for political ends — and share prices rose in Moscow on the news he would be pardoned.

Putin has long singled out Khodorkovsky, who would be due for release in August, for bitter personal attacks, once saying that "a thief should sit in jail."

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

Saying that Khodorkovsky's mother was ill, he added: "I decided that, with these circumstances in mind, we should make a decision to pardon him."

Russian stocks rose by 1.3 percent after Putin's comment, even though his lawyers and mother said he had not asked for a pardon. One of the lawyers said, however, that Putin did not need a pardon request to release him from prison.

Investors had long seen the treatment of a man who built a business empire on the ruins of Soviet communism as evidence of the weakness of property rights and the rule of law in Russia.

Supporters say Khodorkovsky was jailed to curb a political challenge to Putin, bring his oil assets under state control and send a signal to other wealthy "oligarchs" to toe the line. His assets were sold off, mainly into state hands.

In the eyes of Kremlin critics at home and abroad, Khodorkovsky's jailing is one of the biggest stains on the record of Putin, who was first elected president in 2000 and has not ruled out seeking another six-year term in 2018.

Khodorkovsky's mother, Marina, who will turn 80 next year, said she had just heard the reports and was unaware of a request for a pardon.

"I want to believe he will pardon him," she told Reuters. "I want to believe Putin is not totally lost."

Khodorkovsky is due for release in August. But he has previously had his jail term extended on other charges and analysts have said Putin would allow Khodorkovsky to walk free only if he no longer regarded him as a political threat.