A pro-Islamist militant website has issued a post saying Chechen rebel leader Doku Umarov has "become a martyr."
on the Kavkaz Tsentr site gave no details about where or when Umarov died.
There have been reports in previous years that Umarov had been killed, but they were never confirmed and Chechen rebels always denied he had been slain.
This new posting is believed to be the first time that supporters of Umarov have reported his demise.
The information posted on March 18 focused on Umraov's life since 1994, when Umarov "came out for jihad."
A spokesman for Russia's National Anti-Terrorism Committee was quoted by state news agency RIA as saying he could not confirm Umarov was dead.
"Foreign media periodically publish information about the liquidation of Doku Umarov, but the Russian special services at this moment do not have such information and will not comment on it," the agency quoted a committee statement as saying.
The obituary includes a video that features man identifying himself as Ali Abu Muhammad, who says he's Umarov's successor.
Umarov has been held responsible for a series of attacks targeting Russia's government and its allies in Russia's restive North Caucasus region.
Based on reporting by Reuters and RFE/RL