Anzor Astemirov, an associate of rebel leader Doku Umarov, was killed in a shootout with FSB security service troops in Nalchik, capital of the southern Kabardino-Balkaria region, investigators with the prosecutor's office said in a statement.

Astemirov shot at the officers during a routine document check and was killed in a return of fire, the statement said.

Authorities say Astemirov had orchestrated the takeover of Nalchik by a small army of rebels in October 2005. At least 70 militants, 24 police and 12 civilians were killed in what is seen as one of the most brazen attacks in Russia in recent years.

Authorities have claimed a series of successes in recent months following an upsurge of attacks last year in the Muslim-dominated regions of the North Caucasus, which also include Chechnya, Ingushetia and Dagestan.

Law-enforcement officials this month said they killed a senior rebel commander accused of orchestrating a November train bombing that killed 26 and a militant accused of killing an Orthodox Christian priest in Moscow last year.

In recent days Russian-commanded forces said they had killed the top bodyguard of rebel leader Doku Umarov, Abu Khalid, and the leader of his forces in the Chechen capital Grozny.