Officials in Russia say one police officer and three militants have been killed and more than 60 others have been injured in bombings in the volatile North Caucasus region.Two bombs exploded overnight in the centre of Makhachkala, the capital of the Republic of Dagestan, bordering Chechnya. Most of those injured were police officers.The first blast is believed to have been intended to attract people to the area, then a second bomb with an estimated 35 kilograms of explosive detonated.In other violence, a police chief in Dagestan was ambushed and two bodyguards were killed. Dagestan is the most violent of Russia's Caucasus Republics.Militants are fighting for a separate Islamic state in the region and there are attacks on an almost daily basis.