MEXICO CITY (Reuters) – The six migrants who died after Mexican soldiers fired on the pick-up truck they were traveling in were from Egypt, El Salvador and Peru, Mexican President Claudia Sheinbaum said on Thursday.

The killings, which occurred in the southern Mexican state of Chiapas on Tuesday, underscore the tensions on Mexico’s southern border as it faces U.S. pressure to contain migration.

“It’s a regrettable event and it must be investigated and punished,” Sheinbaum said, speaking in her regular morning press conference.

She said the attorney general’s office was investigating the incident.

“A situation like this cannot be repeated,” she added.

Mexico’s defense ministry said the soldiers opened fire after the pick-up truck, which was carrying 33 migrants in total, tried to evade a military patrol.

Another 10 migrants were injured in the incident, the agency said.

The event also shines a renewed spotlight on the growing security crisis in the southern Mexican region near the Guatemalan border, where a territorial battle between powerful drug cartels has led to a sharp increase in violence over the last year.

The defense ministry said soldiers reported hearing explosions before the officers opened fire. Sheinbaum refused to answer questions about the soldiers’ account, saying only that the investigation was ongoing.

(Reporting by Ana Isabel Martinez; Writing by Laura Gottesdiener; Editing by Chris Reese)