Exchange of fire

An interior ministry spokesman said that police were exchanging gunfire with the attackers hours later.

The communications tower had been blown up the night before by unknown assailants.

Criminal gangs, clan violence and fighters opposing the pro-Kremlin regional government cause frequent battles in Dagestan leading to the deaths of scores of civilians.

Islamic groups in the North Caucasus want a separate state.

Dagestan and neighbouring Chechnya and Ingushetia have suffered increased violence during the past few years, a decade after the second of two devastating wars in Chechnya in which Russian forces drove separatists from power. 

A leader of one of the main Chechen groups opposing the regional government claimed responsibility for two bomb blasts in Moscow's metro in March that killed 40 people.

Two days later suicide bombers killed 12 people, mostly police officers, in Dagestan.