Authorities investigating the slaying of nine men at a house in Monterrey, Mexico said today small local drug-trafficking groups appeared to be involved but not major drug cartels. The men were watching a football match on television yesterday when armed attackers burst into the house, herded women into the bathroom and then opened fire on the men, the attorney general of the state of Nuevo Leon, Bernardo Gonzalez, said. Seven men were killed on the spot and two others died of their wounds after being taken to local hospitals, he said. Gonzalez said drugs were found in the house, and the attack appeared to involve local drug traffickers. But in an interview on local television, he insisted, "This is an isolated incident. It has nothing to do with a dispute between cartels in our state." Monterrey, an important industrial centre in northern Mexico, has been shaken by drug violence in recent years, stemming from a conflict between the Gulf and Zeta cartels. Omar Trevino, the Zeta leader known as Z-42 and considered one of Mexico's most ruthless drug bosses, was arrested in 2015 in a posh Monterrey suburb.