An unknown amount of stolen radioactive material has prompted an alert in nine Mexican states, the head of national emergency services said on Monday.
The interior department said the white truck, which was carrying industrial X-ray equipment that uses radioactive material, was stolen on Sunday in Tlaquepaque, a town in Jalisco state.
The missing radioactive material is iridium-192. The agency said on Monday that the material could pose a health hazard if removed from its container and not handled correctly.
It specified that even a brief exposure to the radioactive material could cause "permanent injuries", however the material poses no risk if left in its container.
The alert and search for the stolen material covers the states of Jalisco, Colima, Nayarit, Aguascalientes, Guanajuato, Michoacan San Luis Potosi, Durango and Zacatecas, according to a post on Luis Felipe Puente's Twitter account.
Mr Puente encouraged people with information about the stolen material to report it but added: "don't open it."
There have been several such thefts in Mexico in recent years, but the radioactive materials have been recovered.
The International Atomic Energy Agency (IAEA) has identified radioactive sources, such as iridium-192, used in industrial radiography, radiotherapy, industrial irradiators and thermo-electric generators as those that are the most likely to be used to cause serious radiological harm because they contain large amounts of radioactive material.
Such sources can be used to build "dirty bombs" or radiation dispersal devices, the agency says.
"Such a bomb uses conventional explosives to spread radioactive material that causes injuries and creates social disruption through the evacuation, the subsequent clean-up of contaminated property and the associated economic costs."
The agency has been working for years to increase protection of such materials and the facilities handling them within its member states.