El Salvador condemned on Tuesday the action of detention center staff in Mexico during a fire that killed at least 38 migrants, including “several” Salvadorans, and demanded a thorough investigation.

The migrants from Central and South America were killed in the fire that broke out late on Monday at the migrant center in the Mexican border city of Ciudad Juarez, apparently after a protest over deportations.

A video shared on social media appears to show three people at the center in what appear to be official uniforms failing to open a cell door as the fire began.

"El Salvador expresses its strongest condemnation of the very serious actions of the personnel of the migration station ... during the fire that left dozens of people of different nationalities dead, including several Salvadorans,” the government said in a statement.

"We demand that the relevant authorities thoroughly investigate what happened and bring those responsible to justice.” Mexican President Andres Manuel Lopez Obrador said authorities believed the blaze, one the deadliest migrant disasters in years, broke out after some migrants set fire to mattresses in a protest after discovering they would be deported.

He did not provide more details. The video posted on social media, which appears to be security footage from within the center, shows a flame in part of a cell that is filling up with smoke as men kick desperately on the bars of a locked door. In the 30-second clip, three people in what appear to be official uniforms walk past but make no attempt to open the door.

By the end of the video the smoke is so thick the cell can no longer be seen. Reuters was unable to independently verify the video but Mexican Interior Minister Adan Augusto Lopez, in an interview broadcast on media, appeared to confirm its veracity saying the government had had the video since shortly after the incident, without commenting in any detail on its content.

Foreign Minister Marcelo Ebrard said he had been informed that those“directly responsible” had been turned over to investigators.