"This act confirms that criminal organizations are looking to kidnapping and extortion because they are going through a difficult time obtaining resources and recruiting people willingly," the Mexico's government security spokesman, Alejandro Poire, said at a news conference Wednesday.
All those killed -- 58 men and 14 women -- were believed to have been trying to make their way across the border into Texas, less than 100 miles away from the ranch in San Fernando where the bodies were discovered Tuesday.
The wounded survivor of the massacre made his way to a police highway checkpoint, and marines were sent to investigate. After a shootout in which one marine and three gunmen died, the bodies were found in a large room, some sitting and others piled on top of each other.
The survivor was described by a Quito newspaper, according to Agence France-Presse, as an 18-year-old farmer from Ecuador who paid money to traffickers to smuggle him across the Mexican border. He was identified by the Associated Press as Luis Freddy Lala Pomavilla.
In a statement to police, the survivor said that the group had refused efforts by the drug gang's leader to extort money from them and that gunmen were then ordered to open fire, The New York Times reported.
A report by Agence France-Presse, however, said the Zetas gang offered to pay the migrants $500 a month to work for them and were shot to death when they refused.
The Mexican authorities have confirmed at least seven cases so far this year of drug cartels kidnapping migrants, The Associated Press was told by Antonio Diaz, an official with the National Migration Institute, a think tank that studies immigration.
But the National Human Rights Commission says some 1,600 migrants are kidnapped in Mexico each month, according to the news agency.
A Mexican affairs analyst told the BBC that migrants from South and Central America are frequently targeted by the drug cartels because "they carry large amounts of cash with them in order to pay for the transport and every expense they need to make to reach the border."
The analyst, Miguel Molina, added, "All the drug cartels operating in Mexico also have a role to play in the kidnappings of illegal immigrants and otherwise regular people."
In June, police recovered 56 bodies from an abandoned mine near Taxo, south of Mexico City, and last month 51 corpses were discovered near Monterrey, in the north.
Tuesday's discovery "once again demonstrates the extreme danger and violence that Central Americans face on their treacherous journey north, as well as the Mexican government's abject failure to protect them," said a statement issued by Amnesty International, the AFP reported.