An explosion in the Russian region of Dagestan has killed at least three policemen and at least four other officers are wounded. There are conflicting reports as to the cause of the blast. Some say a a car packed full with explosives was detonated; others suggest a bomb placed close to a police station was set off.The blast took place on one of the main roads through the Dagestani capital. Makhatchkala. The region has suffered from an overspill of violence from nearby Chechnya. It has been has been the scene of numerous bomb and shooting attacks by Chechen rebels. Ten soldiers were killed in a similar blast in Dagestan’s capital in July.