MEXICO CITY — A gang aligned with Mexico’s most wanted drug lord may be delivering a gruesome challenge to the ruling cartel and Mexican officials in the Gulf state of Veracruz, by dumping 35 bodies on a busy avenue in front of horrified motorists and near where the nation’s top prosecutors were about to start a convention.

Authorities said Wednesday they believe the bodies unloaded by gunmen during rush hour Tuesday were people connected with the Zetas cartel, whose presence has grown in the state since a crackdown began last year in their main base of Tamaulipas to the north. A dozen of the victims were women, the state attorney general said.

While Mexican officials would not say who carried out the attack, a banner left at the scene threatened the Zetas and bore the initials “G.N.” A U.S. law enforcement official said that appeared to refer to a group tied to Joaquin “El Chapo” Guzman, widely considered the world’s wealthiest drug trafficker.

But the official, who could not be quoted by name for security reasons, also said it would be surprising to see heavy involvement in Veracruz by Guzman’s Sinaloa cartel, which is based in the Pacific coast state of the same name on the other side of Mexico.

Drug trafficking in Veracruz was long controlled by the Gulf Cartel. But the business has been taken over by the Zetas, who had acted as enforcers for the Gulf Cartel before breaking away in early 2010 and waging a bloody war with their former allies across northeastern Mexico.

“We don’t have anything that corroborates or disputes” that the body dumping was linked to Guzman, the U.S. official said, adding that other sources say the Gulf Cartel could have been responsible. “Sometimes these criminal groups blame the other guys.”

Security expert Raul Benitez agreed it could be possible, however, because Guzman is forming alliances to attack the Zetas in other parts of Mexico. He said Guzman is seeking both to control territory and to punish the Zetas for attacking civilians, something that is shunned by most drug traffickers and that has ramped up government heat on all cartels.

Veracruz, with its major port, is a key route for cocaine passing through Mexico from Guatemala en route to Texas.

Photographs of the bodies showed them handcuffed, bloodied and bruised, some marked with a “Z’’ on their torsos. Veracruz State Attorney General Reynaldo Escobar Perez told MVS radio Wednesday that they had been dead only a few hours.

Escobar, who earlier reported that many of the victims had links to organized crime, said they had records for kidnapping, extortion, murder and drug dealing. He called the killings unprecedented in a state where crime has been escalating dramatically, including deadly attacks on soldiers and journalists.

“The killing of 35 people is deplorable, but it’s even more deplorable the same victims chose to extort, kidnap and kill,” Veracruz Gov. Javier Duarte wrote via Twitter.

Authorities said they were examining surveillance video for clues to who left the 35 bodies beneath an overpass while other gunmen pointed weapons at frightened drivers.

The bodies were left piled in two trucks and on the ground near the statue of the Voladores de Papantla, ritual dancers from Veracruz state.

Printed September 22, 2011 as: Gunmen drop off 35 bodies on active roadway in Mexico