MOSCOW -- A Chechen rebel warlord who has plagued the region for decades and most recently threatened to attack the Sochi Olympics is dead, Chechnya's Kremlin-backed strongman said Thursday, but he offered no proof and his claim couldn't be verified.

Chechen leader Ramzan Kadyrov said on his Instagram that Doku Umarov, who urged his fighters to strike the Games, had died -- a claim he has made repeatedly in the past. The information about Umarov's death came from intercepted communications between other rebel leaders who were discussing his replacement, he said, but he didn't make clear when the conversation took place or how it was heard.

This time, however, multiple messages on Chechen jihadist web forums – including an audio recording from top Islamic sharia judge Abu Mohammed Ali Daghestani, who is affiliated with Umarov’s movement, confirmed his death.

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Messages posted on Chechen militant blog sites suggested he was killed in an operation by Russian special forces, but none gave a time or specific place for the alleged killing.

According to Kadyrov, the insurgents are too busy trying to find a replacement to Umarov to pose any threat to the Olympics that start Feb. 7. "That's why all the talks about the threat to Sochi are absolutely groundless," he said.

The Interfax news agency quoted an unidentified source in Russian security agencies as saying they can't confirm Umarov's death.

Interfax also quoted Kadyrov as saying that Umarov's body hadn't been found but his forces were looking for it.

Umarov is the leader of the so-called Caucasus Emirate, a loose alliance of rebel groups seeking to create an independent Islamic state in Russia's North Caucasus.

He has claimed responsibility for numerous terror attacks in Russia, including suicide bombing in Moscow's Domodedovo airport in January 2011 that killed 37 people and injured more than 180, and twin suicide bombings on the Moscow subway in March 2010 that killed 40 people and wounded more than 120.

In 2012, Umarov ordered a halt to attacks on civilian targets during the mass demonstrations against Putin in the winter of 2011-12. He reversed that order last July, urging his men to "do their utmost to derail" the Sochi Olympics, which he described as "satanic dances on the bones of our ancestors."

Chechnya has become more stable under Kadyrov, who has used lavish Kremlin subsidies for a massive effort to rebuild the region, which was devastated by two separatist wars. He has relied on his feared security force including many former rebels that has been notorious for its brutality. But the insurgency has swept other Caucasus provinces, with Dagestan becoming the new epicenter of the rebellion with near daily shootings and bombings of police and other officials.

On Friday, Fatima Ubaidatova, a spokeswoman for the local police in Dagestan, said unidentified attackers fired a rocket-propelled grenade at a restaurant in the provincial capital, Makhachkala. No one was hurt, but when police arrived at the spot, a bomb placed in a car parked nearby went off. The explosion wounded nine people, including two police officers.

Concerns about the threat posed by the Islamist insurgency in the Caucasus were heightened by back-to-back suicide bombings in the city of Volgograd in southern Russia, which killed 34 and wounded 100 others, on Dec. 29-30. No one has claimed responsibility for the attacks.

Sochi organizers have introduced some of the most sweeping security measures for the Games, which are the top priority of President Vladiimir Putin's presidency. They include the deployment of tens of thousands of police, army troops and other security forces equipped with drones and other sophisticated gear. Anyone wanting to attend the games will have to buy a ticket online from the organizers and obtain a "spectator pass" for access. Doing so will require providing passport details that allow authorities to screen all visitors.