At least four militants were killed in a clash between two rebel groups in the northeast Indian state of Assam Friday, said police. The clash took place in the state's Karbi Anglong district Friday morning. Suspected militants also torched at least 30 houses at seven villages of Rengma tribal community in the district, according to police. The killed belonged to a group called "Rengma Naga Protection Force (RNPF)" by another group called "Karbi People's Liberation Tiger (KPLT)". Top police official rushed to the area and launched an operation against the militants. Tribal and communal clashes take place frequently in Assam, a frontier state inhabited by numerous tribals and ethnic groups. Some militant groups there also stage attacks, kidnapping and murder against government forces and officials from time to time.