Russian soldiers patrol the air defence missile military base stationed near the Olympic park at the Black Sea resort city of Sochi, on November 30, 2013 Credits: Yuri Kadobnov/AFP Russia on Thursday launched a counter-terror operation after five bodies riddled with bullets were found in a southern region bordering the Winter Olympics host Sochi, less than a month before the start of the games.

Two districts in the Stavropol region were placed on high alert after the bodies were found in four cars, one of them apparently booby-trapped, in the area on Wednesday, the Interfax news agency quoted the FSB security service as saying.

As police examined one of the cars, which contained the body of a local resident who had been shot in the head, an improvised explosive device (IED) went off in a nearby ditch, causing no injuries. Officers then defused another device nearby, the FSB said.

A security source told Interfax the two devices were packed with small metal pieces such as screws to cause maximum injury and resembled those previously used by insurgents in southern Russia.

Two other bodies were identified as local taxi drivers and were found in the back seat and in the boot of their Lada cars. The remaining two bodies were found close to a parked car, Interfax cited the FSB as saying.

The Investigative Committee, which probes major criminal cases in Russia, opened investigations into murder, arms trafficking and attempts on the lives of law enforcement officials.

The Stavropol region borders the Krasnodar region where the Black Sea resort of Sochi is located.

Russia on Tuesday launched the largest security operation in Olympic history, a month before the Winter Games kick off on February 6.

Russia particularly fears attacks by Islamist militants from the North Caucasus during the Sochi games, after two suicide bombings at a rail station and in a trolleybus last month in the southern city of Volgograd.

Security measures around Sochi include special permits for cars to enter the city or access Olympic venues, as well as drones monitoring the region and patrols by army troops.