At least 38 migrants from Central and South America died after a fire broke out late on Monday at a migrant detention center in the Mexican northern border city of Ciudad Juarez, apparently caused by a protest over deportations, officials said Tuesday.

Mexico’s National Migration Institute lowered the death toll on Tuesday evening to 38 from 40, saying a visit to the city’s hospitals where victims were being treated had confirmed the lower number, Reuters reported.

Mexican President Andres Manuel Lopez Obrador said authorities believed the blaze in the city opposite El Paso, Texas, broke out around 9:30 p.m. local time (0330 GMT) as some migrants set fire to mattresses in protest after discovering they would be deported. He did not provide more details about how so many had died in the incident.

“They didn’t think that would cause this terrible tragedy,” Lopez Obrador told a news conference, noting that most migrants at the facility were from Central America and Venezuela.

The fire, one of the deadliest migrant tragedies in years, occurred as the United States and Mexico are battling to cope with record levels of border crossings at their shared frontier, read the report.

A video shared on social media, which appears to be security footage from within the center, shows a flame in part of a cell which is filling up with smoke as men kick desperately on the bars of a locked door.

In the 30-second video, 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, read the report.

Reuters was unable to independently verify the video. Interior Minister Adan Augusto Lopez in an interview broadcast on local media appeared to confirm its veracity saying the government had the video since shortly after the incident, without commenting in any detail on its content.

Alejandra Corona, a representative of the Jesuit Refugee Service (JRS) which visits the facility once a week to monitor conditions, confirmed the video showed the men’s cell. The door the men were kicking on was the only exit, she said.

Mexico’s National Migration Institute (INM), which runs the center, did not immediately respond to a request for comment, Reuters reported.

In a statement Tuesday evening, in which the INM revised down the death toll it listed the names of 68 men at the detention center, without clarifying who on the list had or had not survived.

Thirteen of the dead were Hondurans, according to the country’s deputy foreign minister.

A Reuters witness at the scene overnight saw bodies laid out on the ground in body bags behind a yellow security cordon, surrounded by emergency vehicles. The fire had been extinguished.

The migration institute said it was also providing assistance to 15 women who had been safely evacuated from the center when the fire started, read the report.

Foreign Minister Marcelo Ebrard said on Tuesday evening he had been informed that those “directly responsible” had been turned over to the Attorney General’s office, which is investigating the incident. He provided no further details.

Two migrants told Reuters that authorities had rounded up migrants off the streets of Ciudad Juarez on Monday and detained them in the center.

Activists have frequently flagged concerns of poor conditions and overcrowding in detention centers as migration has risen.

“Last night’s events are a horrible example of why organizations have been working to limit or eliminate detention in Mexico,” said Gretchen Kuhner, director of the Mexico-based Institute for Women in Migration, which supports migrant rights.

U.N. spokesman Stephane Dujarric said in a statement that the secretary-general called for a “thorough investigation” of the tragic event.

Mexico’s INM did not respond to a request for comment about when the Ciudad Juarez site was opened, or how many migration centers are currently in operation.

As of 2019, there were 53 INM detention centers operating across Mexico, according to a report from Mexico’s Human Rights Commission (CNDH), with a total official capacity of around 3000.

Viangly Infante, a Venezuelan national, had been waiting outside the center when the fire started.

“I was here since one in the afternoon waiting for the father of my children, and when 10 p.m. rolled around, smoke started coming out from everywhere,” the 31-year-old Venezuelan national told Reuters.

Her husband, 27-year-old Eduard Caraballo, was detained on Monday by Mexican migration authorities and put in a holding cell inside the facility.

He managed to survive by dousing himself in water and pressing against a door as the fire blazed, said Infante.

“His chest was really hurting, struggling to breathe because of all the smoke, but he wasn’t burnt,” said Infante of her husband, who is now in a hospital.

The couple and their three children left Venezuela last October in search of better economic opportunities and a good education for their kids, as well as to escape rampant crime.

By late December, they had reached the U.S. border and crossed into Eagle Pass, Texas, where they handed themselves over to U.S. migration authorities. But they were immediately returned to Mexico, where they then headed by bus to Ciudad Juarez.

Recent weeks have seen a buildup of migrants in Mexican border cities as authorities attempt to process asylum requests using a new U.S. government app known as CBP One, Reuters reported.

Many migrants feel the process is taking too long and earlier this month clashes occurred between U.S. security and hundreds of mostly Venezuelan migrants at the border after frustration welled up about securing asylum appointments.

Mexico’s migration law says migrants can only be detained for 15 days under normal circumstances, though the Supreme Court in March ruled that such lengths were unconstitutional, and that migrants should be held no longer than 36 hours.

In January, the Biden administration said it would expand Trump-era restrictions to rapidly expel Cuban, Nicaraguan and Haitian migrants caught crossing the U.S.-Mexico border in an effort to contain the border flows.

That came after a decision in October to the expand expulsions, under a controversial policy known as Title 42, to Venezuelans.

At the same time, the United States said it would allow up to 30,000 people from those countries to enter the country by air each month, Reuters reported.