A police officer was killed on Saturday in a road bomb in Russia's North Caucasus Republic of Dagestan, a local police official said.

"According to the latest information, one police officer was killed in an explosion that occurred this morning on the road leading to the Dagestan town of Kaspiysk," the official said.

Three police officers were travelling in the car when the bomb was detonated.

"One had minor injuries and was not taken to hospital. The second was concussed and dismissed from hospital. The third, unfortunately, was killed," a Kaspiysk law-enforcement source said.

Earlier on Saturday local police reported that three militants had been killed in the region after they opened fire at police officers during an inspection of the militants' car.

Terrorist attacks and shoot outs with police are common in the volatile North Caucasus, where Russia has held two brutal wars against separatists in the region of Chechnya, which borders Dagestan.

MAKHACHKALA, May 29 (RIA Novosti)