Islamabad, May 16 : At least 16 people were killed and four others injured in an exchange of fire between two rival groups in Pakistan's Khyber Pakhtunkhwa province, police said on Tuesday. The incident occurred late Monday night over the demarcation of a coal mine disputed between two groups in Darra Adam Khel tribal area of Kohat district, police officials told Xinhua news agency. The police said that the firing took place due to a long-standing dispute between the two tribal groups, and that several sessions of Jirga, a local tribal court, had been held to reconcile the rival tribes. However, the groups turned violent when they faced each other while working in the coal mine earlier on Monday. Following the incident, the police and rescue teams immediately rushed to the site and shifted the victims to a nearby hospital, according to the local media. The police have registered a case against the culprits and started investigations. Law enforcement agencies have taken control of the disputed coal mine, said the police, adding that some offenders fled the scene after firing, and a search operation is underway to nab them. /IANS