MEXICO CITY (Reuters) - A clash between armed vigilante groups just north of the resort city of Acapulco killed 13 people on Saturday, according to Mexico's human rights commission.

The violence came on the eve of Mexico's midterm election, in which President Enrique Pena Nieto faces growing discontent over lawlessness, corruption, and lackluster economic growth.

Acapulco, a once-famed tourist hub, has more recently become known as one of Mexico's most violent cities.

One of the two vigilante gangs involved in Saturday's battle is believed to have connections to the Jalisco New Generation cartel, a methamphetamine trafficking group that the government accuses of posing a major threat to public safety.