At least five people were killed at an electronic music festival at a popular Mexican resort on Monday after a lone shooter opened fire, festival organizers said. Rodolfo Del Angel, director of police in the state of Quintana Roo, said another 15 people were injured in addition to the five killed. Del Angel told local media the shooting was caused by “a disagreement between people inside” the club where the festival was underway. The attack happened at about 2:30 a.m. local time in the Blue Parrot nightclub in Playa del Carmen, about 45 miles from Cancun. The Associated Press had earlier cited a Mexican police officer as saying four people had been fatally shot, while DJ Jackmaster, a performer at the event, said “four or five” people had been killed. The police officer spoke on condition of anonymity, as he was not authorized to speak to the press. NBC News cited an employee at the CostaMed hospital in Playa del Carmen saying two people were admitted early Monday with gunshot wounds, with one in grave condition. Several other people were injured in the shooting and had been sent to other hospitals, the employee said, speaking on condition of anonymity.