Two districts in the Stavropol region, which boarders Krasnodar and is located 186 miles east of Black Sea resort of Sochi, have been placed on high alert following the unexplained killings, which also involved booby-trapped cars.

Local authorities said all the victims had been shot dead and when investigators approached one of the vehicles, an explosive device went off close by, while another was made safe.

No one else was injured.

As well as being close to Sochi, the area is just north of the volatile Caucasus Mountains region, where insurgents have been seeking an Islamic state.

It was also targeted in a car bomb attack in late December, which killed three people outside the traffic police offices there.

Russia this week launched one of the biggest security operations in Olympic history ©AFP/Getty Images


Investigators are now working to determine who carried out the killings.

"A counter-terrorism operation has been launched from midnight on January 9 in the Predgorny and Kirov districts of the Stavropol region," the regional administration said in a statement.

The attack follows the deadly double bombing, which killed 34, in the city of Volgograd last month and comes just days after Russia began one of the biggest security operations in Olympic history, with the Games beginning with the Opening Ceremony on February 7.

The Sochi 2014 mass security clampdown measures include special permits for cars to enter the city or access Olympic venues, mail inspections, the implementation of monitoring drones and army patrols.

Meanwhile, Moscow's three international airports yesterday announced a flat ban on all carry-on liquids, including medicines.

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