Three police officers were killed and two more injured when gunmen opened fire on their cars in Russia\'s restive region of Dagestan, investigators said Wednesday. A police major and two other officers were killed on Tuesday evening while driving through Buinaksk, a city about 30 kilometres (18 miles) from the capital of Dagestan, Makhachkala, in Russia\'s North Caucasus. \"Unidentified persons ... opened automatic gunfire\" at the two cars the policemen were travelling in, said a statement on the Investigative Committee website. \"Two more policemen were taken to the hospital with various wounds,\" the statement said. Dagestan, the most populous and ethnically diverse region of the mountainous North Caucasus in southern Russia has become the most unstable in recent years, with rebels staging attacks against the pro-Kremlin local authorities on a nearly daily basis.