Mexican authorities on Friday found a load of dangerous radioactive material that was in a stolen pick-up, a top civil protection official said.
The load of iridium-192 was found abandoned on a street a few miles from where the truck was stolen in the industrial Mexico City suburb of Tlalnepantla, Luis Felipe Puente, the head of the country's civil protection agency, said on Twitter.
Military troops mounted a security perimeter around the small container emblazoned with logos for hazardous materials until it was removed from the site by the country's nuclear safety commission, according to media reports.
The material, normally used in industrial radiography, was housed in a specialized container and would only pose a health risk if the housing was tampered with, Mexico's interior ministry said in a statement.
The truck, which belongs to a metalworking company, had been stolen on Thursday.
In December, thieves in Mexico made off with a truck containing dangerous radioactive medical material -- Cobalt-60 -- that the United Nations' nuclear agency said could provide an ingredient for a "dirty bomb," in which conventional explosives disperse radiation from a radioactive source.
That radioactive load was also found dumped by the thieves close to where it was stolen.
On Saturday the UN International Atomic Energy Agency, which has stepped up calls on member states to tighten security to prevent nuclear and radioactive materials falling into the wrong hands, said that Mexico had informed it about the incident and that it had been told there was no release of radioactivity and no threat to people or the environment.
Because radioactive material is regarded as less hard to find and the device easier to make, experts say a dirty bomb is a more likely threat than a nuclear bomb in a terrorist attack.
However, they say a dirty bomb carries more potential to terrorize than cause a large loss of life.
Nuclear expert Mark Hibbs of the Carnegie Endowment think-tank said Iridium-192, a common medical and industrial isotope with many applications, "in theory" could be used as a radiological weapon.
But, "the perpetrators would have to accumulate enough material to disperse it effectively which may be difficult since in many cases small amounts of Ir-192 are used in sources," he said in an e-mail.
"Unlike cobalt-60, which remains a dangerous source of radiation for many years, Ir-192's shorter half-life implies that perpetrators would have far less time to fashion it into a dispersion device," Hibbs added.