March 18, 2014 -- American and Russian security officials cannot confirm the death of Doku Umarov, also called “Russia’s bin Laden,” as was reported by a militant website linked to the insurgency.

The death of Umarov, who has led a violent campaign against the Russians throughout the Northern Caucasus for years and who most recently threatened the Sochi Olympics, was announced by the "Command of the Caucasus Emirate," according to the website Kavkaz Center. No other details were provided, except that he was “martyred.”

Russia's National Anti-Terrorist Committee said that it had "no information" on Umarov's potential death and would not comment on foreign reports, according to Russia's state-owned RIA Novosti. A spokesperson for the U.S. National Security Council told ABC News the council had seen the report but "cannot confirm" the claim either.

Umarov, the most wanted terrorist in Russia sometimes known as "Russia's bin Laden," has been reported dead several times before, but Kavkaz Center in the past has been used as a mouthpiece for the Islamist leader, lending some credence to the claim. However, Christopher Swift, a Georgetown University professor who has studied militant groups in the North Caucasus, urged caution with regards to the Kavkaz report, saying the website’s connection to the insurgency has been overstated in the past.

If Umarov’s death had been confirmed, Swift said, the Russian government would have little reason to hide it and it would be the biggest story in Russia today -– possibly bigger than the crisis in Crimea -- but the report has so far received scant coverage there.

Umarov has claimed responsibility for deadly terror attacks in Russia in the past, including the January 2011 suicide attack on Moscow's Domodedovo airport, which killed 36, and a bombing of Moscow's metro network the year before, which killed 40 others.

In addition to Russian authorities attempting to hunt him down, Umarov is also wanted by the U.S. and a $5 million reward was offered by the U.S. State Department for information leading to his location starting in 2011.

READ: The Secret Battle Between US Forces and Chechen Terrorists

[Editor’s Note: To Swift’s point, a previous version of this report said Kavkaz Center was “closely” linked to the insurgency. According to Swift, such a link is more tenuous than previously believed.]

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