One policeman and seven civilians were killed when a car bomb exploded in Russia's Muslim North Caucasus province of Dagestan on Wednesday, authorities and local media said.

Three car bombs killed six people and gunmen killed four more, including a high-level law enforcement official, last week in the region wedged between Chechnya and the Caspian Sea.

Dagestan is beset by near-daily shootings and bomb attacks, blamed on an Islamist insurgency across the North Caucasus stemming from two separatist wars in Chechnya, poverty and an increase in radical Islam.

"As a result of the car bomb one policeman was killed, along with five civilians who were travelling past in another vehicle," a source in the regional Investigative Committee told Reuters, speaking on condition of anonymity.

Radio station Ekho Moskvy said two more civilians were killed, including an 11-year-old girl.

The committee source said the attack took place in the village of Hajjalmakhi, about 60 km (40 miles) southwest of the provincial capital Makhachkala.

Upon discovering an empty "suspicious-looking vehicle" parked on the village outskirts, police started to conduct a search when it burst into flames, a law enforcement source told Interfax news agency.

Rebels are fighting for a separate Islamic state ruled by sharia law in the mainly Muslim North Caucasus on Russia's southern frontier.

Russian President Dmitry Medvedev has called the insurgency the country's main security threat in the year before the March 2012 presidential election, which will see Prime Minister Vladimir Putin seek a return to the Kremlin.

The insurgents claimed responsibility for a suicide bombing at Moscow's Domodedovo airport that killed 37 people in January and twin bombings that killed 40 in Moscow's metro last year.