A senior police officer was killed by unknown gunmen in Russia\'s North Caucasus republic of Ingushetia late on Thursday, a police source said. The three gunmen attacked Savarbek Matiyev at his house at 10:50 pm local time (18:50 GMT), the source said. The police officer died at the scene. A criminal case has been initiated over the attack. Militant attacks and clashes remain common in the volatile North Caucasus region although the Kremlin\'s anti-terrorism campaign in the region has officially ended. High unemployment coupled with low living standards are thought to be the main factors driving residents of the North Caucasus to join militant groups.