Unknown assailants opened fire on a military checkpoint in the Russian North Caucasus republic of Dagestan, investigators said.

The attackers, who had arrived inside a Lada Priora hatchback, were killed by return fire, they said.

It was not immediately clear how many attackers there were and whether any troops were injured.

An Islamist insurgency once confined largely to Chechnya has spread in recent years across the North Caucasus, with attacks reported regularly in the neighboring republics of Dagestan, Ingushetia, and Kabardino-Balkaria.