Two police officers were killed when a car exploded at a traffic-police post in the North Caucasus republic of Daghestan, Russian media report.
Another two police officers were reported injured in the February 15 incident in the Derbent district.
Seventeen people were injured in the blast, 14 of whom have been hospitalized. At least five of the injured are reportedly in serious condition.
An investigation is under way, but preliminary findings indicate a gas canister may have been used in the blast. A local police official said it was "a rather large explosion" and "could have been perpetrated by a suicide bomber."
Daghestan is beset by deadly violence linked to an Islamist insurgency that is rooted in two post-Soviet separatist wars in neighboring Chechnya.
Organized crime, business turf wars, political disputes, and clan rivalry also contribute to the bloodshed.
Moderate Muslims, journalists, police, and government officials are regularly targeted in attacks.