Authorities on the Gulf coast of Mexico said the bodies of seven men have been found dumped on a roadway in the Huasteca region, long popular among tourists.
Prosecutors in San Luis Potosi state said late Thursday the bodies did not appear to be from the township of Aquismon, and may have been killed elsewhere and dumped in the rural area.
Photos of the bodies showed extensive bruising on the corpses, suggesting they had been beaten.
Writing scrawled in markers on the corpses said “this is what happened to me for working with the Gulf,” an apparent reference to the Gulf Cartel, which operates mainly along the U.S. border to the north.
The messages were signed “Valles Operation O.B.,” apparently a reference to a rival gang.
The Huasteca region has long been popular with Mexican tourists for its waterfalls and crystalline rivers.
Last month, the Justice Department said that former Gulf Cartel leader Mario Cardenas-Guillen was extradited to Texas on drug trafficking charges.
The cartel uses “intimidation and extreme violence to maintain control of its territories in northeast Mexico and smuggle deadly drugs into communities across the United States,” DEA Administrator Anne Milgram said.
According to a recent report by the Congressional Research Service, the Gulf Cartel was the main competitor challenging Sinaloa for trafficking routes in the early 2000s, but it now battles its former enforcement wing, Los Zetas, and Zeta Cartel splinter groups over territory in northeastern Mexico.
Mexico has seen a recent spate of deadly violence linked to cartels and gangs.
On Tuesday, gunmen killed five high school students and a woman in a street shooting in Guanajuato state, an area where gangs fight for control of trafficking routes for drugs and stolen fuel.
Two weeks before that, eight women and three men were killed in an apparent gangland revenge attack on two bars and a hotel in Celaya, another city in Guanajuato.
Since December 2006, when the government launched a controversial military anti-drug operation, Mexico has recorded more than 340,000 murders, according to official figures.
Authorities have blamed most of the killings on organized crime.
In April, President Andres Manuel Lopez Obrador confirmed that Mexico had dissolved a special unit trained by U.S. authorities to fight drug cartels because it had been infiltrated by criminals.