Russia has put security forces on combat alert in the southern Stavropol region, about 150 miles northeast of Sochi, after the discovery of five bodies with gunshot wounds and an explosive device, a regional security spokesman said.
Russia has already tightened security before next month's Winter Olympics in Sochi, on which President Vladimir Putin has staked his political and personal prestige, and is on high alert after suicide bombers killed at least 34 people in separate attacks in the southern city of Volgograd last month.
The five corpses were discovered on Wednesday in four cars in two separate districts outside the regional capital, Stavropol, a gateway to the North Caucasus, where Russia faces an insurgency by Islamist militants who have threatened to try to prevent the Olympics from going ahead.
An unidentified explosive device was found near one of the vehicles, said a spokesman for Russia's Federal Security Service (FSB) in Stavropol. No other details were immediately available.
Putin said after the Volgograd attacks that he would annihilate all "terrorists" in Russia.
The Winter Olympics open in Sochi on Feb. 7. The Black Sea resort is on the western edge of the Caucasus mountains where the insurgents want to carve out an Islamic state.
The head of Russia's Olympic Committee has said no more can be done to safeguard the games because every possible measure is already in place.
Russian forces went on combat alert in Sochi on Tuesday, and about 37,000 personnel are now in place to provide security at the games, Russian officials said.