Russia has rarely used air power against militants in recent years, said Tatyana Lokshina, who researches the North Caucasus with Human Rights Watch.  “It’s a huge operation by Russian standards,” Ms. Lokshina said, though she cautioned that the effectiveness of such assaults could be difficult to gauge.  Officials offered a measured assessment of the operation, saying only that they suspected that several militant commanders had been killed.  “Among the dead militants there should be the leaders of militant groups,” Nikolai Sintsov, a spokesman for Russia’s National Anti-Terrorist Committee, said Tuesday. “At the moment, an investigation is under way to determine the identities of the dead criminals.”  Several Russian news agencies, citing anonymous law enforcement officials, said that Doku Umarov, the self-proclaimed militant leader who has claimed responsibility for a string of attacks, might be among the dead. But there was no official confirmation.  In any case, the Investigative Committee, Russia’s top investigative agency, filed charges against Mr. Umarov on Tuesday for his role in a suicide bombing in January at Moscow’s Domodedovo airport that killed at least 35 people.  Mr. Umarov had previously taken responsibility for that attack, as well as for the subway bombings in Moscow last year, but had never been officially charged with a crime.  The Investigative Committee also released new details on Tuesday about two brothers arrested recently and charged with accompanying the suicide bomber in the Domodedovo attack.  Officials announced the arrest of the brothers, Islam and Ilez Yandiyev, on Monday. When detained, they had in their possession a suicide belt and two bombs, the agency said in a statement on its Web site.  “The presence of the explosive devices,” the agency said, “leads to the conclusion that they were preparing a terrorist attack.”  A version of this article appears in print on March 30, 2011, on Page A8 of the New York edition with the headline: Medvedev Warns Islamic Separatists. Order Reprints| Today's Paper|Subscribe
A day after an air attack on what officials called a militant base in the North Caucasus region, President Dmitri A. Medvedev of Russia warned separatist fighters to surrender or “be destroyed.”