Mexico City , Mexico ( CNN ) -- Mexican investigators have asked diplomats from El Salvador , Honduras , Ecuador and Brazil to help identify the bodies of 72 presumed migrants discovered at a ranch in northeast Mexico . The nationalities of the deceased have not yet been confirmed , according to a statement released by Mexican President Felipe Calderon 's office late Wednesday . Brazil said its Foreign Ministry was informed there were at least four Brazilians among the dead , the official Agencia Brazil news service reported Wednesday evening . There was no further information about the identity of the dead Brazilians or exactly how many had been killed , the government-run news agency said . The statement by Calderon said the Mexican president `` strongly condemns the acts that caused the death of 72 people , suspected to be migrants , '' and said that drug gangs are repeatedly turning to extortion and kidnapping of migrants as their resources and recruits dwindle . `` This is a result of the activity of the state against them , which has significantly weakened the operational capacity of criminal groups , '' Calderon 's office said . Initial reports indicated the migrants were headed to the United States . A surviving immigrant said he and the others were shot when they refused to work for a cartel , news reports said . It was not clear whether the cartel was smuggling the migrants or had abducted them . The Center for Strategic and International Studies , a bipartisan , nonprofit policy institute based in Washington , noted in an August report that human smuggling and other illegal activities are playing an increasingly important role as narcotraffickers diversify their activities . `` The drug cartels have not confined themselves to selling narcotics , '' the report said . `` They engage in kidnapping for ransom , extortion , human smuggling and other crimes to augment their incomes . '' And the risk is increasing for Central and South American migrants crossing through Mexico to get to the United States , said Mexico 's National Commission for Human Rights . An investigation by the commission showed that 9,758 migrants were abducted from September 2008 to February 2009 , or about 1,600 per month . The bodies of the 58 men and 14 women discovered Tuesday were found above ground in a building on the ranch , which is about 14 miles ( 22 kilometers ) from the town of San Fernando , near the border with Texas . The Mexican navy , which was called in to investigate the case , said it is one of the largest discoveries of bodies in Mexico 's 4-year-old war on organized crime . Members of the Mexican navy were tipped off to the site after a man with a gunshot wound approached a military roadblock . The man said he had been injured by a criminal gang , according to a statement released by the navy . Mexico 's attorney general 's office identified the man as an Ecuadorian immigrant and said he had a bullet wound to the neck . `` The navy went to the area where the man came from and encountered gunfights . A naval officer was killed and three of the delinquents were killed , '' said an officer who answered the telephone at the navy 's communication department . The officer , who was not authorized to speak on the record , declined to give his name . After the gun battle , authorities said , they found a stash of weapons , including 21 rifles , camouflage uniforms , bulletproof vests and four trucks . One of the vehicles had been disguised to look like a truck from the Ministry of National Defense , officials said . A preliminary investigation indicated the victims were illegal immigrants from Honduras , El Salvador , Brazil and Ecuador , said Alejandro Poire , spokesman for national security strategy . `` This discovery once again demonstrates the extreme danger and violence that Central Americans face on their treacherous journey north , as well as Mexican authorities ' abject failure to protect them , '' Amnesty International said . `` Mexico must immediately investigate this massacre , bring the perpetrators to justice and establish the identities of those killed so that their families can be informed . '' Wednesday 's gruesome discovery came about a month after authorities in the neighboring state of Nuevo Leon discovered 51 bodies in nine mass graves . In that instance , investigators found charred remains , incinerated bone fragments and stains of fire on the ground where bodies were presumably burned in steel drums , the state-run Notimex news agency said . Similar mass graves have been discovered in the Mexican states of Guerrero and Quintana Roo since late May . Authorities have linked them to Mexico 's ongoing drug war . Nuevo Leon and Tamaulipas , which border Texas , have seen a marked increase in drug violence this year due to an intensifying rivalry between the Gulf cartel and the Zetas gang , which was formerly the cartel 's armed branch . More than 28,000 people have died in drug-related incidents since Calderon intensified the government 's fight against drug cartels and organized crime after taking office in December 2006 .
NEW : The attackers are believed to be Central and South American migrants crossing Mexico . Brazil says at least two Brazilians were among the dead . Mexico says they are extorting migrants as Mexican government weakens cartels . Two policemen and a member of the Mexican military were killed in a shootout .