Russia has put security forces on combat alert in the southern Stavropol region after the discovery of five bodies with gunshot wounds and an explosive device.
It has already tightened security before the Winter Olympics in Sochi, after suicide bombers killed at least 34 people in separate attacks in the southern city of Volgograd in December, Reuters reports.
A regional security spokesperson said the corpses were discovered on Wednesday in four cars in two separate districts outside the regional capital of Stavropol. The explosive device was found near one of the vehicles.
The city is a gateway to the North Caucasus, where Russia faces an insurgency by Islamist militants who have threatened to try to prevent the Olympics going ahead.
The head of Russia's Olympic Committee has said no more can be done to safeguard the Games, which start on 7 February, because every measure possible is already in place.
Russian forces went on combat alert in Sochi on Tuesday and about 37,000 personnel are in place to provide security at the Games, officials say.