At least 11 people were killed and another dozen injured when gunmen opened fire on locals who had gathered at a football pitch in the city of Salamanca in central Mexico on Sunday.

Witnesses said armed men arrived at the grounds in several vehicles and shot at those gathered there seemingly indiscriminately. Many families had stayed behind to socialize after a match between local clubs. At least one woman and one child were among those killed.

The motive behind the shooting is not yet clear. Guanajuato, the state in which Salamanca is located, registered the highest number of murders in the whole of Mexico last year.

Neighbours reported hearing at least 100 shots ring out as the gunmen opened fire at the Cabañas pitch in the Loma de Flores neighborhood. Local and federal security forces are now investigating the deadly shooting, which came a day after five men were killed and another was abducted in the city.

Guanajuato has seen a rise in violence due to gang warfare, including theft of oil and drug trafficking activities. Salamanca, with its major Pemex refinery, has been particularly affected by violent gang-related attacks.

Analysts point to the rivalry between the Jalisco New Generation Cartel (CJNG) and the Cartel de Santa Rosa de Lima (CSRL) as the cause of many brutal incidents. The U.S. has recognized the CJNG as a Foreign Terrorist Organization and placed sanctions on both gangs, intensifying efforts to combat the drug-related violence spreading into the United States.