At least four police officers have been killed and six others injured after Somali policemen turned on each other and clashed in the war-ravaged Somali capital of Mogadishu, Press TV reports. Residents said police forces exchanged heavy gunfire in the Nasteho area of Wadajir district on Friday after policemen patrolling the area got into an argument, and opened fire on each other. Four policemen were killed instantly on the spot, while six others sustained injuries at various levels. “A group of police officers shot dead a fellow policemen at a checkpoint in Nasteho area after they argued. A few minutes after the shooting, several policemen arrived at the scene and fired indiscriminate shots at the former police officers,” Abdi Sheikh, an eyewitness, told Press TV. He added that the gunfight did not last long, and soon subsided. “I saw the dead bodies of four policemen lying on the street after the infighting. Six injured policemen were also close to them,” Sheikh noted. Meanwhile, Somali police spokesman Abdullahi Hassan Barise said that an investigation into the deadly incident has been launched. Somalia has not had a functioning government since 1991, when warlords overthrew former dictator Mohamed Siad Barre. The weak Western-backed transitional government in Mogadishu has been battling al-Shabab fighters for the past five years and is propped up by a 12,000-strong African Union force from Uganda, Burundi, and Djibouti.