Four security officers were injured when unknown gunmen attacked their car in Russia’s volatile North Caucasus republic of Dagestan, police said.

A roadside bomb went off on a highway to the south of the republican capital, Makhachkala, as the police truck was passing by. The gunmen then opened fire on the vehicle from a nearby forest.

“Four security officers received various traumas and contusions,” a police spokesman said.

The troubled North Caucasus region sees frequent attacks on government officials, police and security forces as Moscow battles an Islamist insurgency there.