MOSCOW, February 14 (RIA Novosti) – A fourth policemen has now been reported killed following a suicide car bombing in Russia’s North Caucasus republic of Dagestan on Thursday.

Previously, the police said three officers and the bomber died when he detonated explosives as the police stopped his car at a checkpoint outside the city of Khasavyurt around 5 a.m., local police said. Another policeman reported as missing was later found dead. Six injured policemen were rushed to hospital.

The blast left “a crater four meters in diameter and 1.5 meters deep,” the Investigative Committee reported in a statement. The explosives contained between 100 and 120 of TNT, according to the Investigative Committee spokesman Vladimir Markin.

The police forces ambushed suspected rebels linked to the attack not far from the blast scene, killing at least four of them, the Interior Ministry reported.

The policemen had been posted to Dagestan from the Vologda region, some 1,800 km north of Dagestan. The Investigative Committee has opened a criminal case on terrorism charges. No-one has yet claimed responsibility for the attack.

The police forces clashed in a shooting with suspected rebels linked to the attack and ambushed not far from the blast scene, police reported later on Thursday.

Dagestan and most of the neighboring North Caucasus has suffered years of armed conflict between Islamist insurgents and the security forces, with frequent bombings and shootings.

(Updated at 13.20 and 18.11 with the death toll rising to four and killed suspected rebels)