Four police officers were killed and another was injured in a suicide bomb attack in Russia's North Caucasus republic of Chechnya on Tuesday, Russian news agencies reported. A suicide bomber detonated a home-made explosive device hidden under his clothing when he approached five policemen who were waiting for their vehicle to be cleaned at a car wash, RIA Novosti quoted a local police source as saying. Four police officers were killed on the spot and a fifth policeman has been hospitalized with severe wounds, the source said. In a separate report, Interfax quoted a local official source as saying that the blast in Chechnya's Shali region left four policemen and two passers-by dead and another policeman wounded. The attack is the latest in a spate of violence in the restive North Caucasus region. Suicide bombers on bicycles killed four police in coordinated attacks in the Chechen capital of Grozny on Friday. At least 25 people died and over 160 were injured in last Monday's suicide bombing of a police station in neighboring Ingushetia. In April, the Kremlin formally ended an anti-terrorist operation in Chechnya, which has experienced two bloody wars in the past 15 years. 