Nine states have been placed on high alert after radioactive material capable of producing a dirty bomb were stolen near the Texas-Mexican border this week.
The Mexican government say that Iridium-192 could be used to make a device that would contaminate a wide area with radioactive material.
“The source can be dangerous if it is not handled in safe conditions,” a spokesman said for the Ministry of the Interior.
“It could cause permanent injuries to anyone who manipulates it or is in contact with it over a short period of time. Plus if the material is not in its container it represents a significant risk to health.”
The urgent search for the stolen material covers the states of Jalisco, Colima, Nayarit, Aguascalientes, Guanajuato, Michoacan San Luis Potosi, Durango and Zacatecas,.
Iridium 192, which has a half-life of 73 days, is one of a small number of radioactive materials suitable for use in an act of radiological terror.
But authorities are concerned the radioactive isotope may have been stolen accidentally, with thieves unwittingly holding onto the destructive material after attempting to steal the pickup truck it was housed in.
Lord Browne, vice chairman of the Nuclear Threat Initiative, said that when IS captured Mosul in 2014 it claimed to have taken caesium from hospitals.
He said: “I do not know if that was true but the fact that they said it reveals that they know the terror threat that it poses.”
He added: “There is significant intelligence that terrorists around the world know these materials exist, know where they are and have been making efforts to get them.
“In a terrorist investigation in Norway the authorities discovered that the person of interested wanted to do this. Norway acted immediately by removing the material from hospitals.
“I don’t think there’s an intelligence brief in the world that does not suggest that a dirty bomb is not a threat or that terrorists have not expressed a desire to get their hands on the material.”