Mexican marines patrolling a lake along the border with Texas discovered a drug gang camp on an island, provoking a gunbattle that left 13 people dead, the navy said Monday.
Investigators in a different northern state reported finding 11 decapitated bodies and exhumed 22 remains from mass grave sites where they have found 179 dead people since last month.
One marine and 12 suspected gunmen of the Zetas drug cartel were killed in the battle Sunday on Falcon Lake in the northeastern state of Tamaulipas, the navy said in a statement.
The navy said the gunmen opened fire first when the marines discovered the camp, which the gang is believed to have used as a launching point for smuggling marijuana into Texas by speedboat. Marines seized more than 20 guns after the shootout, including several assault rifles.
Falcon Lake, a dammed section of the Rio Grande, is where U.S. citizen David Hartley was presumably chased and gunned down by pirates Sept. 30. His body has not been found and Mexican investigators have reported no leads in the case.
His wife, Tiffany Hartley, told authorities she and her husband were using personal watercraft on Falcon Lake when they were approached by pirates who shot and killed her husband. The couple, who lived in nearby McAllen, Texas, at the time, were returning to Texas after photographing a historic church on the Mexican side of the lake, Hartley said.
Mexican officials called off a search for David Hartley on Oct. 14, but the case remains open.
The search was hampered when authorities received threats, presumably from the Zetas. The Tamaulipas state police commander and chief investigator of the Hartley case, Rolando Flores, was killed while the search was under way, his decapitated head delivered in a suitcase to a local Mexican army post.
Mexican authorities say they don't know whether Flores' killing was related to the Hartley case because he had been in charge of several investigations.
The Zetas are locked in a fierce turf battle with the Gulf cartel that has turned much of Tamaulipas state into a virtual war zone. Last month, security forces discovered more than 40 clandestine graves containing 183 bodies. Many of the victims had apparently been pulled off passenger buses by Zetas gunmen trying to recruit them.
A similar discovery was made last month in the northern state of Durango, another drug cartel battleground. Soldiers unearthed 22 more bodies _ among them three women and 14 men _ from mass graves in the capital of Durango city over the weekend, bringing the rapidly mounting toll to 179, according to statements Monday from the Durango state attorney general's office.
The Mexican army will continue excavating at a mass grave site Tuesday.
President Felipe Calderon's security spokesman, Alejandro Poire, said Monday that "the finds were a result of a capture made by federal forces."
Poire said investigations into the mass grave sites revealed that the motives of the Durango killings were different than in Tamaulipas, but he did not explain or give any specifics.
Besides mass grave sites, there is public display of drug violence in the vast, mountainous state. The decapitated bodies of 11 men were found Monday in two places in Durango, the state attorney general's office said.
Agents first discovered six decapitated men across from a middle school in the capital, which is also named Durango. Investigators then found five decapitated men on a highway that connects Durango to the Pacific resort of Mazatlan. The heads lay next to the bodies.
The attorney general's office has not identified the bodies or the motives for the killings.
Associated Press writer E. Eduardo Castillo contributed to this report.