Some 27 people, more than half of those identified among the dead, were from Mexico. Another 14 were Hondurans, seven were from Guatemala, and two people from El Salvador also died, Mexico's government said.

A pair of Guatemalan boys aged 13 and 14 were among those to have perished in the accident, officials from their home country announced on Wednesday.

Pascual Melvin Guachiac and Juan Wilmer Tulul were cousins who left home two weeks ago in order to escape poverty, Pascual's mother was quoted in Guatemalan media as saying.

On Monday, just hours before the lorry was discovered abandoned, the teenage relatives had told their family that they were headed for San Antonio.

According to Mexican immigration officials, the migrants most likely crossed the border in smaller groups before gathering in a secret safe-house inside the US, where they would have been crammed into the lorry for the next stage of their journey.

Those inside the lorry were found sprinkled with a pungent substance, the officials added, as part of a method used by some smugglers to mask the scent of human beings and avoid being detected by canine patrols.