Poverty and desperation” led to the deaths of at least 50 migrants abandoned in a Texas lorry, Mexico’s president has said.
Andres Manuel Lopez Obrador blamed trafficking and “a lack of control” at the border – the worst case of migrant deaths due to smuggling in the US.
Nearly two dozen Mexicans, seven Guatemalans and two Hondurans were among the dead.
Those found alive, including four children, were taken to hospital.
The survivors were “hot to the touch” and suffering from heat stroke and heat exhaustion.
So far, Mexican authorities have said that at least two Mexican citizens are being treated for dehydration in hospital. Consular officials are working to confirm their identities.
Authorities are working to confirm the nationalities of remaining victims.
According to US authorities, three people “believed to be part of the smuggling conspiracy” have been taken into custody.
Speaking at his daily briefing, Mr Lopez Obrador, popularly known as Amlo, called the discovery a “tremendous tragedy”, and said Mexico would work to repatriate the remains of its citizens.
This and other migrant deaths were due to the “poverty and desperation of our Central American brothers, and of Mexicans,” he said, adding: “It happens because there is trafficking of people and a lack of control, in this case at the Mexican-US border, but also in the US interior”.
Mexico’s Foreign Minister, Marcelo Ebrard, said that Mexico has joined the probe and is sending a team to Texas to help with the investigation.
The White House called the truck deaths “horrific and heart-breaking”.
The migrants were found on the outskirts of the city of San Antonio, which is 250km (155 miles) from the US-Mexico border, is a major transit route for people smugglers.
Human traffickers often use trucks to transport undocumented migrants after meeting them in remote areas once they have managed to cross into the United States.
“They had families… and were likely trying to find a better life,” San Antonio Mayor Ron Nirenberg said. “It’s nothing short of a horrific, human tragedy.”
Written by BBC America
