The bullet-pocked bodies of 72 people, believed to be migrants heading to the United States who resisted demands for money, have been found in a large room on a ranch in an area of northeast Mexico with surging violence, the authorities said Wednesday. Initial reports after the victims were found Tuesday suggested that the mass of bodies was the largest of several dumping grounds -- often with dozens of dead -- discovered in recent months and attributed to the violence of the drug business. If the victims, found after a raid on a ranch in Tamaulipas state by Mexican naval units, are confirmed as migrants, their killings would provide a sharp reminder of the violence in human smuggling as well. It was not clear if the victims, from Central and South America, were shot all at once. The police were relying on a harrowing but sketchy account from a wounded survivor, published by the newspaper Reforma and confirmed by government officials, who said several people were killed in short order after the migrants refused to pay or cooperate with the gunmen. A law enforcement official said all were found in a large room, some sitting, some piled atop one another. Alejandro Poire, the government's spokesman for security issues, said that though the investigation was just beginning, the killings seemed to be an outgrowth of pressure on drug gangs by a government crackdown. '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,' Poire told reporters here. U.S. law enforcement officials have warned that drug trafficking groups have increasingly moved into the lucrative business of human smuggling, extorting fees from migrants for safe passage across the border and sometimes forcing them to carry bundles of drugs. Smugglers are also known to rob, kidnap and sometimes kill migrants on both sides of the border. The unidentified survivor, an Ecuadorean traveling with people from Ecuador, Brazil, Honduras and El Salvador, told investigators that the migrants had entered Mexico from the south and that they were making their way to Texas when they were confronted by the gunmen in San Fernando, about 100 miles south of Brownsville, Texas. In a statement to the police, he said the leaders of the armed group had tried to extort fees from them and, when the migrants resisted, ordered their gunmen to open fire. Wounded in the neck by the gunfire, the survivor heard screams and pleas for mercy. Once the men retreated, the witness said, he ran from the ranch where they were being held Monday and found a military checkpoint. The military units reached the ranch Tuesday and engaged in a firefight in which one marine and three suspects were killed. The authorities said 58 men and 14 women had been killed in the room by the gunmen. It was unclear how long they had been dead or held by the group. The discovery of the bodies was the largest of at least three such finds this year. In May, 55 bodies were pulled from an abandoned mine south of Mexico City, and in July, 51 bodies were discovered in a field near Monterrey, an industrial and commercial hub in northeast Mexico that had been relatively quiet until this year. A shootout last week in Monterrey outside the American School Foundation, a private school popular with American expatriates and Mexican business executives, prompted the U.S. Consulate to advise families to keep their children home pending an assessment of security at the school. More than 28,000 people have been killed in drug-related violence since President Felipe Calderon began a crackdown on organized crime in 2006. In a meeting with mayors Wednesday, Calderon said, 'We're in the middle of a criminal spiral that we have to cut.' 'I don't know of any crime that isn't organized,' Calderon said. 'They are all very organized, and much more than the police.' 