Chechen rebel leader Doku Umarov, who claimed the Moscow Metro bombings earlier this year which killed 40 people, is said to be resigning.
In a video released online a man appearing to be Mr Umarov, 46, says he is handing over to a younger comrade.
The speaker says a man seated next to him, named as Aslambek Vadalov, can lead "more energetically".
Doku Umarov is one of the few rebel leaders to survive from Chechnya's spell of independence from Russia.
He served as security minister in the separatist government from 1996-99.
The Russian state regards him as a notorious terrorist, head of the self-styled Caucasus Emirate - an armed Islamist movement seeking control of the mainly Muslim territories in the Russian North Caucasus.
He is also officially described as a terrorist by the US state department.
In the video, which appeared on a French video-sharing website before being removed on Sunday, the man believed to be Doku Umarov says he will continue personally to wage "jihad" against Russian rule in the Caucasus.
BBC News
