Russia has been the key ally of Syrian President Bashar Assad, protecting him from the United Nations sanctions and providing him with weapons in the civil war, which has killed more than 93,000 people since March 2011.
Some observers have voiced concern that militants from the Caucasus who joined the Syrian rebels could try to take revenge against Russia for its support of Assad and try to strike 2014 Winter Olympics in Sochi.
Russian officials have pledged to make the games "the safest Olympics in history," but security experts warn that the Islamist insurgency that has spread across Russia's North Caucasus after two separatist wars in Chechnya could threaten Sochi, located about 500 kilometers (300 miles) west of Dagestan.
Earlier this month, a top Chechen rebel warlord called on militants to disrupt the Sochi Games, which he described as "satanic dances on the bones of our ancestors."
Dagestan has become the epicenter of the Caucasus insurgency, with rebels mounting nearly daily attacks on police and other officials.
One of the two ethnic Chechen brothers from Russia who are accused of staging the Boston Marathon bombings spent six months last year in Dagestan. Russian investigators have been trying to determine whether he had contact with local rebels.