The bodies of 35 people with links to organised crime have been found in two abandoned lorries on a highway underpass in eastern Mexico, authorities say.
The bodies were discovered on Tuesday near a shopping centre in Boca del Rio, adjacent to the port city of Veracruz, Reynaldo Escobar, the attorney general of Veracruz state, told the television station Milenio.
"These were people involved in organised crime," he said of the victims, seven of whom have been identified.
He told a local radio station on Wednesday that they had been dead for only a few hours.
Al Jazeera's Franc Contreras, reporting from Veracruz, said "the bodies were piled up... showing marks of torture, while body parts were also found".
Two newspapers, Milenio and La Jornada, said some of the bodies had their hands tied and showed signs of torture.
Photographs of the bodies showed them handcuffed, bloodied and bruised, some marked with a "Z" on their torsos.
All 35 victims, who included 12 women and two minors, were linked to the Zetas cartel, according to an official in the Mexican armed forces, who couldn't be quoted by name for security reasons.
A banner left with the bodies criticised the Zetas for killing innocents and charging extortion, warning: "No more". The banner also bore the initials "GN."
New Generation link
A US law-enforcement official said the New Generation was believed to be linked to Joaquin "El Chapo" Guzman, widely considered the world's wealthiest drug trafficker.
But the US official, who also could not be quoted by name for security reasons, said it would be surprising to see heavy involvement in Veracruz by Guzman or his Sinaloa cartel, which is based in the Pacific coast state of the same name on the other side of Mexico.
"We don't have anything that corroborates or disputes" that the body dumping was linked to Guzman, the US official said.
He suggested that other sources say the Gulf Cartel could have been responsible, saying: "Sometimes these criminal groups blame the other guys."
A Mexican official said the New Generation gang had been carrying out what it called "surgical" attacks that target Zetas only and no civilians.
Raul Benitez, a security expert, agreed that the attack could be the work of a gang aligned with Guzman, who is forming alliances to attack the Zetas in other parts of Mexico.
He said Guzman was seeking both to control territory and to punish the Zetas for attacking civilians, something that was shunned by most drug traffickers and that had ramped up government heat on all cartels.
The Zetas have been blamed in two of Mexico's biggest mass killings of civilians since the federal government stepped up a crackdown on organised crime in 2006: the massacre last year of 72 migrants in Tamaulipas and a casino fire last month in the northern industrial city of Monterrey that killed 52 people, mostly women.
Under Guzman, Sinaloa has grown bloodier and more powerful, controlling cocaine trafficking on the Mexican border with California, while expanding eastward to the corridor between Sonora and Arizona and waging a fierce battle for Chihuahua state bordering Texas.
Mexico's most powerful drug cartel also appears to be expanding methamphetamine production on a huge scale, but has not been known to operate along the Gulf of Mexico coast.
In a separate incident on Wednesday, soldiers clashed with armed men in the northeastern border state of Nuevo Leon, killing five, authorities said.
Troops were on patrol in the town of Cienega de Flores when they came across the men travelling in a 4WD vehicle, a state police investigator said, speaking on condition of anonymity because he was not authorised to talk about the case.
About 42,000 people have been killed since Felipe Calderon, the Mexican president, launched a campaign against drug cartels at the beginning of his term in late 2006.
Most of that violence has been focused on the northern border with the US.