At least 20 people were killed in a Sunday night shootout in Michoacan, a western Mexican state plunged into violence by clashes between rival drug gangs. An attack at a venue often used for hosting illegal betting on cockfights in the town of Las Tinajas was reported to the state attorney general at around 10:30 pm (0430 GMT Monday). The attorney general’s office said the lifeless bodies of 16 men and three women were found at the scene, all bearing gunshot wounds. It later said an additional person had died en route to hospital, while another five were being treated for injuries. Michoacan’s public security office said authorities were working to track down those responsible for the bloodshed. Mexico has been trapped in a spiral of cartel-related violence since 2006, when the government launched a controversial anti-drug operation with federal troops. The violence has since claimed more than 340,000 lives, most of them lost to organized crime, according to official figures. Michoacan and neighboring Guanajuato are two of Mexico’s most violent states due to turf wars between rival gangs involved in drug trafficking and other illegal activities, such as trade in stolen fuel. Several powerful drug-trafficking gangs such as the Jalisco New Generation and Los Viagras cartels operate in Michoacan and battle each other for control of strategic territory.