A Mexican Federal Police officer stands guard as members of a drug gang are loaded onto a helicopter
The Mexican government accused the Zetas drug gang of killing 116 people whose corpses have been found in a series of mass graves near the US border, reports AFP.
Police have detained 17 suspects and believe gunmen from the notoriously violent cartel dragged the victims off buses passing through the San Fernando area of north-eastern Tamaulipas state.
"We can confirm that a total of 116 people have been found dead as a result of criminal actions apparently caused by actions by the Zetas criminal group," Attorney General Marisela Morales told reporters.
Los Zetas, founded by deserters from the Mexican special forces and thought to have many corrupt former officials and ex-police on its payroll, is at the heart of the narcotics trade and organised crime in Mexico.
Engaged since February 2010 in a turf war for control of lucrative smuggling routes into the United States with the Gulf Cartel -- its former employers -- the cartel was blamed for the massacre of 72 migrants in August in Tamaulipas.
Mexican officials say that, aside from drug smuggling, the Zetas use extortion and kidnapping to raise money.
The largest concentration of graves ever found in Mexico was unearthed on Thursday in the San Fernando area, about 160 kilometres (100 miles) south of the Texan border, and the grisly toll has been rising steadily ever since.
Tamaulipas state officials said at least six buses have been attacked by gunmen this year and several passengers kidnapped. Residents told local media the real toll is far higher.
Officials said two buses known to be missing were carrying mostly Mexicans. However, Guatemala's Foreign Ministry said one of the bodies found in the graves was that of a 44-year-old Guatemalan man.
Separately, the US consulate in the Tamaulipas city of Matamoros said at least one American was kidnapped while travelling in one of the held-up buses.
Tamaulipas Governor, Egidio Torre Cantu met in Mexico City with Interior Minister, Francis Blake to discuss the killings.
The Mexican military says the graves were discovered thanks to a tip obtained from a suspect identified as Armando Morales Uscanga.
According to Morales Uscanga, several of those killed were travellers aboard two long-distance passenger buses kidnapped between March 24 and March 29.
Morales Uscanga acknowledged "his participation in the assassination and illegal burial of 43 bodies," the military statement said.
Investigators uncovered the mass graves starting on April 1, after responding to complaints of buses being stopped and passengers abducted.
Los Zetas were also blamed back in August 2010, when officials in San Fernando found the remains of 72 people, mostly Central American migrants, who had been executed by criminals.
Authorities suggested the drug cartel was seeking to recruit young men into their gang and simply killed those who refused.
Some 35,000 people have been killed since 2006 when President Felipe Calderon launched a clampdown on the country's powerful gangs, involving tens of thousands of troops.