MEXICO CITY (Reuters) – The theft of an unknown amount of radioactive material has prompted an alert in five Mexican states, the head of national emergency services said on Wednesday.

The alert and search for the stolen material covers the northern states of Nuevo Leon, Tamaulipas, San Luis Potosi, Zacatecas and Coahuila, according to a post on Luis Felipe Puente’s Twitter account.

Puente encouraged people with information about the stolen material to call authorities, but added that it should not be opened if found. Local media reported that the material had been stolen from an engineering school in Nuevo Leon.

Stolen or lost radioactive material has on several occasions been reported in Mexico, most recently in April.