At least four policemen have been killed when a car bomb exploded in a southern Russian city on Friday, Russian news agencies reported.

A car laden with explosives blew up near a community center in downtown Nazran, the largest city in Russia's North Caucasus republic of Ingushetia, RIA said, citing local police sources.

Two vehicles caught fire and several people were injured on spot when the accident occurred at about 7:15 PM Moscow time (15:15 GMT), police sources said.

The explosion, however, was caused by the collision of two vehicles, Itar-Tass cited a source at the Ingush Interior Ministry as saying.

"A traffic police vehicle collided with a civilian sedan," the anonymous source said.

But a high-ranking officer at the Ingush Interior Ministry said later Friday that it was a terrorist attack.

The explosion occurred when the police cruiser was passing by the parked vehicle, which was loaded with a remotely controlled bomb equivalent to two kilograms TNT, Itar-Tass quoted the officer as saying.

The Ingushetia republic was neighboring the Chechen republic and the two regions were both suffering from year-long terrorist activities.

(Xinhua News Agency September 1, 2007)