PARIS (AP) — Required safety standards weren't met at a vacation home for adults with disabilities where a heavy fire left 11 dead in eastern France, a deputy prosecutor said Thursday.

A day earlier, the fire killed 10 adults with slight intellectual disabilities and one person accompanying them.

Nathalie Kielwasser, the deputy prosecutor of Colmar, said the first phase of the investigation shows that a mandatory safety inspection for such private accommodation facility had not been done.

Speaking on French news broadcaster BFM TV, she said the fire started from the upper floor, but its cause has not been determined.

The building in the Alsacian town of Wintzenheim was equipped to receive 28 people, including 12 on the ground floor and 16 on the upper floor, she added. It was equipped with smoke detectors, she added.

The disabled adults were on a vacation sponsored by two specialized associations. They were staying in the building, whose ground floor was made of stone and the upper part of the building was constructed of wood with heavy timbers in the traditional style of the region — a factor that might partly explain why the fire spread so quickly..

The local administration of the Haut-Rhin region said the fire broke out at 6:30 a.m on Wednesday.

Only five of those who were sleeping on the upper floor managed to escape, authorities said. All twelve people who were staying on the ground floor were able to evacuate.

No details about the victims were provided. Investigators were working on identifying the bodies via DNA testing, Kielwasser said.

It was the deadliest fire in France since an August 2016 blaze that killed 14 people in a basement nightclub in the western city of Rouen.