(AP) — An overnight fire raced through a dormitory in Guyana, killing at least 19 students who were trapped and injuring several others at a government boarding school as authorities probe whether it was intentionally set. All but one of the victims were Indigenous girls, officials said Monday.

“This is a horrific incident. It’s tragic. It’s painful,” President Irfaan Ali said, adding that his government was mobilizing all possible resources as he requested help from the region to identify the remains of 13 bodies.

The fire broke out at about 10:50 p.m. Sunday in the dormitory building of a secondary school that serves remote, mostly Indigenous villages and is  located in the border town of Mahdia, a gold and diamond mining community about 200 miles (320 kilometers) south of the capital, Georgetown, the government said in a statement.

Deputy Fire Chief Dwayne Scotland said “the fire was maliciously set” and began in the building’s southwest corner. However, Police Chief Clifton Hicken said “initial investigations suggest that it was maliciously set.” He also said that while the girls’ dorm had five doors, iron grill work trapped the students inside.

Authorities did not provide further details and did not share what evidence, if any, points to arson.

“This is the saddest day of my life as president. I wish it had not occurred,” Ali said.

A total of 59 girls usually reside in the dorm, but only 56 were in the rooms when the fire began because three of them went home for the weekend. Thirteen girls and a small boy died at the dorm, while five died at Mahdia Hospital, the government said.

Of those injured, six children were flown to Georgetown and 17 remain hospitalized in Mahdia, officials said.

Officials initially said 20 students were killed but later updated the toll to 19, with several others injured. National Security Adviser Gerald Gouveia said the figure was revised after doctors revived a very critical patient that “everyone thought was dead.”

“When firefighters arrived on the scene, the building was already completely engulfed in flames,” Guyana’s Fire Service said in a statement. “Our heartfelt sympathy goes out to the relatives and friends of those young souls.”

Officials said two children remain in critical condition and four have severe injuries.

“Firefighters did manage to rescue some 20 students by breaking holes in the northeastern wall of the building,” the department said.

The school serves mostly Indigenous children aged 12 through 18, Gouveia said. He said it was too early to speculate what might have caused the fire, adding that heavy thunderstorms in the area posed a challenge to those responding by air.