Investigators in Russia's southern Dagestan republic say a car has exploded at a police checkpoint, killing two officers and injuring at least two others.

The local branch of the federal Investigative Committee says it is still unclear what caused the Russia-made Lada Priori to explode Monday morning at the checkpoint in the Derbent region.

Dagestan has been the center of an Islamic insurgency that spread across the Caucasus region after two separatist wars in neighboring Chechnya. For more than a decade, Dagestan has seen bombings, attacks on police and kidnappings blamed on the Islamic militants.

In recent years, however, the republic has grown markedly less violent as hundreds of militants have left to join the Islamic State group in Syria.