Security services in the southern Stavropol region were put on combat alert on Thursday, after police found several cars with dead bodies inside and explosives planted nearby, security officials said.
The series of attacks around two districts of the Stavropol region heightened concerns about security at the Winter Olympic Games in Sochi, 250 kilometers away, that are scheduled to begin in less than a month.
Police found four cars at the scene on Wednesday with the bodies of five people killed by gunshot wounds in the trunks or on the seats, the Stavropol branch of the Federal Security Service said, Interfax reported.
When police arrived to investigate one of the killings, a homemade bomb went off 20 meters away from the car, but nobody was hurt, the security service, or FSB, said. Another explosive device was defused by a bomb disposal robot, the statement said.
The authorities declared a "counter-terrorism operation regime" starting at midnight on Thursday in the Kirov and Predgorny districts, where the cars had been found, and security services went on combat alert, the FSB said.
Two of the shooting victims have been identified as young local men, who appeared to have been moonlighting as gypsy cab drivers, police spokesman Yevgeny Arnautov said.
Police have opened an investigation into possible charges of murder, illegal dealing in explosives and an attempted attack on law-enforcement officers.
Russia has been beefing up security throughout its southern regions and the North Caucasus for months, ahead of the Sochi Olympics. But a series of recent bombings in Volgograd, located 700 kilometers from Sochi, underscored the continuing threat of terror during the Winter Games.
At least 34 people were killed by two apparent suicide bombings in Volgograd on Dec. 29 and 30, following an earlier suicide bombing on a bus in October.
In the Stavropol region, police arrested a man wearing an explosive-packed belt in November.