Police in Russia's restive province of Dagestan says a suicide bomber has killed three policemen and injured six others at a traffic police post in northwest of the province.

Dagestan's police spokesman Vyacheslav Gasanov said Thursday that an unidentified driver blew himself up after officers at the post just outside the town of Khasavyurt asked him to pull over.

The Investigative Committee said in a statement on Thursday that it estimated the bomb to have contained between 100 and 120 k (220-265 pounds) of TNT.

Russia's North Caucasus and Dagestan in particular has for years been plagued by Islam-inspired insurgency which spread throughout the area after two separatist wars in Chechnya.