Police arrested seven alleged drug-gang hit men carrying assault rifles in the resort city of Acapulco, and blamed the easy availability of guns along the U.S. border for a wave of killings.
The recent bloodshed - including a man who was gunned down in Acapulco and an armed assault on a hospital in Tijuana on Wednesday - is also caused by increasing power struggles within and between Mexican cartels, said Patricio Patino, assistant secretary of public safety.
The seven men arrested in Acapulco were members of the Sinaloa cartel and part of a group "dedicated to exterminating Zetas," Patino said, referring to the armed enforcers of the rival Gulf cartel.
Police seized seven assault rifles, several pistols and more than 1,000 rounds of ammunition from the suspects.
"The escalation of violence we are seeing ... (and) the power of these criminal gangs comes from the ease with which they get weapons" on the northern border, Patino said. "Their firepower is impressive."
Patino said the country's drug gangs have also strengthened by branching out into other crimes such as migrant and weapons trafficking, auto theft and kidnapping, and by muscling their way into legitimate businesses.
A bloody turf war between the Sinaloa and Gulf cartels has been blamed for most drug violence in the last four years, but Patino said the Gulf cartel is also in the midst of a growing internal battle between longtime Zeta leader Heriberto Lazcano and power-hungry newcomers.
He pointed to recent shootouts in Veracruz and the arrest earlier this week of Nabor Vargas, a former soldier and alleged founder of the Zetas, as signs of the struggle. Vargas allegedly turned to kidnapping after the cartel's chain of command was weakened by accused gang leader Osiel Cardenas' extradition to the United States in January.
Patino said the old strategy of hunting top cartel leaders had run up against the gangs' ability to reorganize. "They regrouped and regained strength very rapidly," he said. "These are very dynamic organizations."
He said police are now seeking to go after the gangs' enforcement, logistics and financial structures from the ground up.