Homeland Security Secretary Alejandro Mayorkas on Sunday warned migrants “not to take the dangerous journey” and attempt to cross the US-Mexico border after 53 migrants died in a sweltering semitruck in San Antonio, Texas, last week, in what is being called the deadliest human smuggling incident in US history.

“We have said repeatedly, and we continue to warn people not to take the dangerous journey,” Mayorkas told CBS News in an interview. “We saw so tragically in San Antonio, Texas, one of the possible tragic results of that dangerous journey, and so many people don’t even make it that far in the hands of exploitative smugglers.”