A notorious gang leader in Russia's North Caucasus known as Alexander Tikhomirov or Said Buryatsky has been killed in a special operation, law enforcement sources said Thursday.

RIA Novosti has not yet received official confirmation of Tikhomirov's death, but the sources said he was killed on Tuesday and identified on Thursday.

Investigators say Tikhomirov was one of the key ideologists among the militant groups in Russia's volatile south. They also say he organized a number of large-scale terrorist attacks.

Police said Tuesday that at least six suspected militants were killed during a police sweep in the southern Russian republic of Ingushetia.

Fierce fighting had erupted earlier in the day near the region's largest city, Nazran, when a group of heavily armed militants were holed up in several houses and refused to surrender.

According to police, the militants had been involved in recent attacks on law enforcement officials, and planted bombs near police headquarters in Ingushetia.

Russia's mainly Muslim North Caucasus republics, especially Chechnya, Dagestan and Ingushetia, have seen an upsurge of militant violence lately, with frequent attacks on police and officials.

The Kremlin has pledged to wage "a ruthless fight" against militant groups but also acknowledged a need to tackle unemployment, organized crime, clan rivalry and corruption as causes of the ongoing violence in the region.

Moscow announced an end to its decade-long antiterrorism campaign against separatists in Chechnya in April 2009, but has since had to step up the fight against militants as skirmishes and attacks on police and other officials have continued.

MOSCOW, March 4 (RIA Novosti)