MEXICO CITY (Reuters) - Three soldiers died and three more were wounded in a gun battle with suspected gang members in a southwestern Mexican state mired in drug violence, the army said in a statement on Wednesday.

After receiving an anonymous tip on Tuesday that there were armed men at the “El Pozo” ranch, near Coyuca de Benitez in the state of Guerrero, soldiers stationed nearby went to the location, where unknown assailants opened fire on them, the army said. Three died and three more were wounded in the gun fight.

The ranch belonged to the family of Abel Montufar, the former mayor of Coyuca de Benitez, who was shot dead on Tuesday, the Guerrero state coordination office said in a statement. Montufar had left his post to run for state congress as a ruling Institutional Revolutionary Party candidate.

At least 18 politicians have been killed in Guerrero since last September, state authorities say, with violence rising in the run-up to the July 1 presidential election.

Guerrero has become one of Mexico’s top opium-growing regions, sparking violent turf battles between local gangs.

In a TV interview, Guerrero state security spokesman Roberto Alvarez said the rise in U.S. consumption of fentanyl, a powerful artificial opioid, had lowered local opium prices, forcing local gangs to diversify and seek new, often-violent forms of income.