The death toll of migrants found on Monday inside a sweltering 18-wheeler in San Antonio, a major city in south central U.S. state Texas, has risen to 53 after two more migrants died, according to the Bexar County Medical Examiner's Office on Wednesday.
Of the dead, 40 were male and 13 were female, the office said.
Authorities said the tragedy saw the highest ever death count from human trafficking near the U.S.-Mexico border.
Francisco Garduno Yanez, the head of Mexico's National Immigration Institute, told a press conference on Wednesday that at least 27 victims were from Mexico, 14 from Honduras, seven from Guatemala and two from El Salvador. Three victims' nationalities remain unknown.
The tractor trailer with fake plate was carrying 67 migrants, said Garduno.
The driver of the vehicle, identified as Homero Zamorano, 45, has been taken in federal custody after he abandoned the vehicle in a desolate area and fled the scene, according to the San Antonio Express News.
Two other men, both Mexican citizens, were charged on Tuesday with possessing firearms while residing in the United States illegally, according to court documents and U.S. authorities. Police arrested them at an address in San Antonio listed on the tractor-trailer's registration.
Texas Republican Governor Greg Abbott told another press conference on Wednesday that the state will immediately start additional truck checkpoints to target trucks like the one found in San Antonio.
The state will deploy two strike teams, each consisting of 20 troopers, to high-traffic crossing areas, said the governor.
Hours after the migrants were found dead in the truck on Monday, Abbott blamed the deaths on what he called U.S. President Joe Biden's "deadly open border policies."
"Exploiting vulnerable individuals for profit is shameful, as is political grandstanding around tragedy," Biden said in a statement on Tuesday.
The president said initial reports showed that the tragedy was caused by smugglers or human traffickers.
Death is a constant risk for undocumented migrants entering Texas, said a report by The Texas Tribune, noting that in 1987, 2003 and 2017, groups of migrants died of heat and dehydration in Texas after being trapped in stifling containers.
According to the report, hundreds more die alone or in smaller groups as desperation drives them to take fatal risks.
The U.S. Customs and Border Protection said it encountered a record number of 239,416 people along the U.S.-Mexico border in May.
The latest tragedy is "another sign that America lacks a humane, sensible immigration policy," the Wall Street Journal has commented.