CIUDAD VICTORIA: Mexico sought help from Latin American nations Thursday to identify 72 presumed migrants murdered near the US border, after blame for the massacre fell on a brutal drug gang.

Diplomats from Honduras, El Salvador, Ecuador and Brazil arrived in the northeastern state of Tamaulipas to help identify victims found blindfolded, bound and stacked against a wall inside a ranch warehouse.

"The autopsies and identification of bodies have started based on documents carried by some of the victims," a spokesman for the Tamaulipas attorney general`s office told AFP.

But officials struggled to identify many of the 58 men and 14 women because they did not carry documents, said Salvadoran ambassador to Mexico Hugo Castillo.

A Mexican migrant shelter said it was supplying photographs of guests who stayed at its hostels and the military stopped vehicles for any leads on the killings.

The US State Department vowed to "cooperate fully" to help Mexico investigate what it called "heinous crimes."

An injured Ecuadoran man claiming to be the massacre`s sole survivor alerted the military to the ranch, where he said the group had been kidnapped and killed by Zetas drug gang members for refusing to work for them.

Mexican marines discovered the corpses after clashing with suspected drug gang members near the town of San Fernando late Tuesday.

The grisly discovery was the latest mass dumping of bodies in recent months, but unlike other cases blamed on the drug gangs, the corpses this time appeared to have been killed in a single massacre and not over time.

Marines also captured an "underage suspect" at the ranch, but the rest of the surviving gunmen escaped.

A photograph of the 18-year-old survivor lying wounded in a hospital bed was released, prompting Ecuador`s government to express concern for his safety.

The presumed survivor`s 17-year-old wife said she last spoke with him two months ago and wanted to see him to believe he was alive.

The woman, who is four months pregnant, said that when they last spoke, her husband said he was in Guatemala, on his way to Los Angeles.

Mexican President Felipe Calderon strongly condemned the killings, blaming them on a power struggle between the Gulf gang and the Zetas, their former allies.

The increasingly powerful Zetas include former elite Mexican soldiers who deserted the military. The US government has called them the most dangerous organized crime syndicate in Mexico.

Drug gangs are using "extortion and kidnapping of migrants as a means for financing and recruitment because they are struggling to get money and people," a statement from Calderon`s office said.

It pointed to what it claimed was the success of a controversial government clampdown on organized crime, which has seen violence spike, with more than 28,000 deaths in three and a half years despite the deployment of thousands of soldiers.

The case "will turn into an emblem of the capacity or incapacity of Mexican officials to face up" to migrant abuses, said Amnesty International Mexico director Alberto Herrera.

Around half a million clandestine migrants cross Mexico each year, mostly from Central America, according to Mexico`s Human Rights Commission.

Some 10,000 undocumented migrants were abducted in the country in the six-month period from September 2008 to February 2009, the commission reported last year.

Last week, Calderon accused the US government of failing to tackle drug addiction in the United States and neglecting to rein in the arms industry -- the main supplier of weapons to Mexico`s violent drug gangs.

BDST: 10:04 HRS, August 27, 2010