X-Rays Find 513 U.S.-Bound Migrants Hiding In Trucks (VIDEO)

TUXTLA GUTIERREZ, Mexico -- Police in Mexico's southern Chiapas state found 513 migrants on Tuesday inside two trailer trucks bound for the United States, and said they had been transported in dangerously crowded conditions.

Some of the immigrants were suffering from dehydration after traveling for hours clinging to cargo ropes strung inside the containers to keep them upright as the trucks bounced along from the Guatemalan border, and allow more migrants to be more crammed in on the floor.

The trucks had air holes punched in the tops of the containers, but migrants interviewed at the state prosecutors' office said they lacked air and water. The trucks were bound for the central city of Puebla, where the migrants said they had been told they would be loaded aboard a second set of vehicles for the trip to the U.S. border.

"We were suffering, it was very hot and we were clinging to the ropes," said Mario, a 23-year-old Honduran migrant who identified himself only by his first name, for security reasons. Mexico's National Human Rights Commission says thousands of undocumented migrants are kidnapped and held for ransom by drug gangs in Mexico each year.

None of the migrants would say whether any drug gang had been involved in the mass smuggling scheme broken up early Tuesday when Chiapas state police discovered the migrants while using X-ray equipment on the trucks at a checkpoint in the outskirts of city of Tuxtla Gutierrez.

The migrants said the smugglers were charging them about $7,000 apiece to get them into the United States. A Guatemalan migrant who identified himself as Juan said remaining in his hometown in Guatemala was not an option, noting "a lot of us are Indians, and we can't stay in our homes. There is no work, and there's nothing to eat."

An agent for the National Immigration Institute who was not authorized to be quoted by name said it was the largest shipment of migrants detained in Mexico in recent years.

Police also arrested four people accused of smuggling the migrants, who are from Central and South America and Asia, Chiapas state prosecutors said in a statement.

The alleged smugglers tried to escape police but were chased down and captured, prosecutors said.

The immigration institute said in a statement that 410 of the migrants were from Guatemala, 47 from El Salvador, 32 from Ecuador, 12 from India, six from Nepal, three from China and one each from Japan, the Dominican Republic and Honduras. There were 32 women and four children among them.

In January, Chiapas state authorities discovered 219 migrants squeezed into a trailer truck.

Most of those migrants were from Central America but six were from Sri Lanka and four from Nepal.