The deaths once again highlight the challenge of controlling migrant crossings at the U.S.-Mexico border, which have reached record highs.

    The issue has proven difficult for U.S. President Joe Biden, a Democrat who came into office in January 2021 pledging to reverse some of the hardline immigration policies of his Republican predecessor Donald Trump. Republicans have criticized Biden's border strategy ahead of the midterm congressional elections in November.

    Mexico's Foreign Minister Marcelo Ebrard called the suffocation of the migrants in the truck the "tragedy in Texas" on Twitter and said consular officials would go to the hospitals where victims had been taken to help "however possible."

    A spokesman for the Honduran foreign ministry told Reuters the country's consulates in Houston and Dallas would be investigating the incident. Ebrard said two Guatemalans were hospitalized and Guatemala's foreign ministry said on Twitter that consular officials were going to the hospital "to verify if there are two Guatemalan minors there and what condition they are in."

    The I-35 highway near where the truck was found runs through San Antonio from the Mexican border and is a popular smuggling corridor because of the large volume of truck traffic, according to Jack Staton, a former senior official with ICE's investigative unit who retired in December.

    In July 2017, 10 migrants died after being transported in a tractor-trailer that was discovered by San Antonio police in a Wal-Mart parking lot. The driver, James Matthew Bradley, Jr., was sentenced the following year to life in prison for his role in the smuggling operation.

    Staton said migrants have regularly been intercepted in the area since the 2017 incident. "It was only a matter of time before a tragedy like this was going to happen again," he said.