Relatives grieve for a victim of a fire at a rehabilitation clinic in Lima, Peru, on Saturday.

Story highlights

NEW: 26 people were killed in the fire

NEW: A mattress fire may have started the blaze

NEW: It may have been a clandestine facility, the fire chief says

CNN —  

Twenty-six people were killed and 15 were rescued from a fire at a rehabilitation center in Lima, Peru, the state-run Andina news agency reported.

The fire was controlled by firefighters by Saturday afternoon.

The cause of the fire was under investigation, the fire department said, though witnesses said a mattress was set on fire during a melee inside the building.

The victims were trapped inside the building and died from asphyxiation, Peru’s fire chief, Antonio Zavala said.

The building may have been a clandestine rehabilitation center, and many people were concentrated on the first floor, which lacked escape routes, Zavala said.

Some 40 people were housed in a small space with only one exit that was locked with a chain. Bypassing the heavy metal door was the biggest challenge in the rescue, he said.