In a separate incident in the violence-torn Caucasus region on the Caspian Sea, two people who may have been planning an attack were killed when explosives in their car blew up.

Vasily Naumochkin, deputy mayor of Kizlyar, north of Dagestan’s main city Makhachkala, came under fire from a car as he was driving to work, the spokesman for regional investigators, Nizam Radzhabov, told AFP.

He was taken to hospital seriously wounded and was undergoing an operation, he added.

“He was wounded in the stomach,” Radzhabov said.

A medical source told the ITAR-TASS news agency that the official’s kidneys and liver had been damaged and he had lost two litres of blood.

A dozen people were killed in Kizlyar in a suicide bombing in March. That attack came two days after bombings on the Moscow metro carried out by two female suicide bombers killed 40.

In a separate incident, two people, a driver and passenger, were killed when an explosive substance ignited in their car overnight close to the village of Gubden in Dagestan, the Interfax and RIA Novosti news agencies reported.

“It is believed that the explosives went off inside the car. It is possible that this was a so-called suicide belt,” an official told the Interfax news agency.

Suicide bombers strap such explosives-laden belts to their chests.

The latest unrest comes after Russian security forces at the weekend shot dead a man suspected of being the mastermind of the Moscow metro attacks in a shootout in Dagestan.

Magomedali Vagabov — the number two figure in the Islamist-inspired insurgency that has plagued the North Caucasus over the last years — was also reportedly married to one of the Moscow metro female suicide bombers.

Russia has in recent years been fighting an increasingly deadly Islamist-fuelled insurgency in the North Caucasus regions of Chechnya, Dagestan and Ingushetia which has claimed scores of lives annually.