Houston, Jun 30 (IANS): The death toll of migrants found inside a sweltering 18-wheeler in San Antonio, a city in Texas close to the US-Mexico border, has increased to 53 following two more fatalities, according to authorities.

Of the dead, 40 were male and 13 were female, Xinhua news agency quoted the Bexar County Medical Examiner's Office as saying on Wednesday

Authorities said the tragedy on Monday saw the highest ever death count from human trafficking near the US-Mexico border.

Francisco Garduno Yanez, the head of Mexico's National Immigration Institute, told reporters 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 number 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 US illegally, according to court documents and American authorities.

Police arrested them at an address in San Antonio listed on the tractor-trailer's registration.

Texas Governor Greg Abbott told the media on Wednesday that the state will immediately start additional truck checkpoints to target vehicles like the one found in San Antonio.

The state will deploy two strike teams, each consisting of 20 troopers, to high-traffic crossing areas, he added.

Hours after the migrants were found dead in the truck on Monday, Abbott blamed the deaths on what he called 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 the state 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 US Customs and Border Protection said it encountered a record number of 239,416 people along the border in May.