Six men were found dead in four abandoned cars in southern Russia this week, authorities said.

While explosives were rigged in three of the cars, investigators said the six victims were shot and only one bomb had gone off without hurting anyone, The Associated Press reported.

Three of the men have been identified, according to Russian state news agencies, although their names have not yet been released. Two of the identified victims were taxi drivers, and the third built furniture for a private businessman.

All three were reportedly local residents who drove inexpensive, Soviet-model Lada vehicles. Their bodies were found in three different cars.

The other three men, who have not yet been identified, were found in a fourth vehicle on Wednesday. Investigators defused an explosive found near the car in a metal bucket, officials said.

The bodies were found Wednesday close to the Caucasus Mountains. Federal Security Service officers are investigating, but no motive has been yet determined, spokesman Vladimir Markin of Russia's main investigative agency told the AP.

The incident increased security concerns as the country prepares to host the Winter Olympics in Sochi next month.

The city was put under a special security regime akin to martial law on Jan. 7, TIME reported. Sochi and its suburbs will be on lockdown for the next two months as more than 30,000 police officers and Interior Ministry troops work to prevent a possible terrorist attack.

"It is certainly not an atmosphere of celebration here," Vladimir Kimaev, a local businessman and environmental activist, told TIME. "It's more a feeling of resignation to wait this thing out and then get on with life."

The Games are planned for Feb. 7-23, but to be on the safe side, President Vladimir Putin ordered the security regime to last until March 21.

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