The death toll from a fire at a day care center in northern Mexico rose to 43 on Monday as the governor of the State of Sonora vowed to investigate how the incident originated.

Another ten children are still in severe condition in hospitals. Many of the victims died from intoxication, according to the Health Department.

The fire, which took place in Hermosillo, Sonora on June 5 apparently started at a storage area near the day care center and expanded. At the time of the incident there were 142 children there ranging from the ages of four months to five years.

Teachers and neighbors helped to rescue the children but 31 died that day, according to media reports. Only six adult staff were at the day care center when the fire broke out, the reports stated.

We will get to the bottom of things. It is our responsibility. The 43 children who died deserve it, Gov. Eduardo Bours told national network Televisa today.

According to a witness, the fire originated after an explosion in a storage area but official reports have not confirmed this.

Bours said the government run center seemed to have all the permissions and security needed. However it was in no way located where it should have been, the governor said, referring to the center’s proximity to industrial buildings. The city council declared three days of mourning for the toddlers, according to Once Noticias.

Some other children with severe burns were taken to specialized health centers including two children who were taken to Shriners hospital in Sacramento, California.