The migrants were crammed into a trailer in the midst of a heatwave in Mexico, where higher-than-normal temperatures have topped 45°C in several states, including Veracruz, where the operation took place.

Immigration agents in late May had uncovered another 175 migrants further south, mainly from Central America, in Chiapas state. Another 300 people were stopped at a checkpoint in Veracruz in March.

Migrants fleeing violence and poverty in Latin America frequently pay smugglers in an attempt to pass through Mexico bound for the US. Some are forced to cross areas rife with drug violence, making them vulnerable to organised crime.

Among the travellers found on Friday were adults from Guatemala, Honduras, India and El Salvador, and 19 unaccompanied minors, the migration institute said.

It added that the children will be put under state guardianship, while the others will be processed to determine their legal status in Mexico. Four suspected traffickers were arrested in the operation.

On Friday the commissioner of the INM, Francisco Garduño, had met with Guatemalan officials to discuss reparations for the victims of a deadly March fire in a migrant detention centre in Mexico that claimed 39 lives, the INM said in a separate statement.