Tatarstan is a predominantly Islamic autonomous republic within the Russian Federation.
"The gunmen were killed in the police assault on the building," Russian Investigative committee member Vladimir Markin said. "They were suspects in the recent attacks on Muslim leaders in Tatarstan."
Russian officials fear the turmoil in the northern Caucasus will spread to the wider areas of the Russian Federation, where Chechen attacks since 2001 have bedeviled the efforts of Moscow to quell the insurgency, Panarmenian.net online news agency reported Wednesday.
Markin said the suspects were surrounded in a building in Tatarstan's capital, Kazan, and offered substantial resistance, killing a Russian security officer and injuring two others in a grenade blast. He said the suspects refused to surrender during the gun battle.
Following the operation, Russian police said they found three handguns, ammunition, and parts of improvised explosive devices at the scene. One of the militants was reportedly wearing a belt containing explosives.