Mexican prosecutors have launched criminal proceedings against top immigration officials as they investigate a fire that killed 40 migrants in a detention center last month, the Attorney General's office said on Tuesday.

The people include the head of Mexico's National Migration Institute (INM), Francisco Garduno, and the agency's top representative in the northern state of Chihuahua where the fire occurred, Salvador Gonzalez, said two sources familiar with the matter.

INM did not immediately respond to a request for comment, and Garduno could not be reached directly. Gonzalez said he would cooperate with the investigation and support the victims.

The Attorney General's office said in a statement it had launched criminal proceedings against six public officials in connection with the fire, identifying them only by first name, as is customary in Mexico.

It did not specify whether the people had been charged or would face charges, and neither the office nor INM provided additional details.

The statement said Garduno and another high-ranking official, identified by the two sources as Antonio Molina, allegedly failed to “watch over, protect and ensure safety for the people and facilities in their charge,” and allegedly facilitated “crimes against migrants.”

Molina could also not be reached directly for comment. The fire came after warnings from the federal auditor over problems inside INM, and concerns from the National Human Rights Commission over a migrant's death at a different detention center in 2020.

"They indicate a pattern of irresponsibility,” the Attorney General's office said. The statement also alleged that Gonzalez and three other officials were linked to conduct that led to the deaths of the migrants.

Earlier Tuesday, President Andres Manuel Lopez Obrador said the migrants had been unable to escape the fire because the person with the key to their locked cell was absent.

Five people were arrested in the case last month, including INM agents and a private security guard. Neither INM nor the security company commented on the arrests