Mexico's nuclear safety director says a stolen container of radioactive material has been found empty.
Juan Eibenschutz says radioactivity has been detected about 1 kilometre from where the stolen truck and empty container were found in the state of Mexico.
He says authorities have cordoned off the area.
This is a breaking news update. Read AP's earlier story below.
A cargo truck hauling extremely dangerous radioactive material from used medical equipment was stolen from a gas station in central Mexico, and authorities sent out an alert in six central states and the capital to find it, Mexican officials said.
The truck was carrying a metal container of cobalt-60 headed to a nuclear waste facility in the state of Mexico, said Juan Eibenschutz, director general of the National Commission of Nuclear Safety and Safeguards. Though the container is heavily sealed in lead, designed to be difficult to break and to survive accidents intact, he said it contains an amount of radioactive material that could do serious damage if opened.
Direct exposure would result in death within a few minutes, he added.
"This is a radioactive source that is very strong," Eibenschutz told The Associated Press on Wednesday, adding that it can be almost immediately fatal, depending on proximity. "The intensity is very big if it is broken."
Eibenschutz didn't know the exact weight, but that it was the largest amount stolen in recent memory, and the intensity of the material caused the alert. Local, state and federal authorities, including the military, are searching for the truck.
The material was used for obsolete radiation therapy equipment that is being replaced throughout Mexico's public health system. It was coming from the general hospital in the northern border city of Tijuana, Eibenshutz said. The thieves most likely wanted the white 2007 Volkswagen cargo vehicle with a moveable platform and crane.
Eibenschutz said there is nothing so far to indicate that the theft of the material was intentional or in any way intended for an act of terrorism.
The thieves likely didn't know what the truck was carrying, he said, and may have discarded the metal container, which he said is about a meter square.
"If someone finds a big chunk of metal with radiation symbols all over it, they should notify us immediately and don't open it," Eibenschutz said.
The truck marked "Transportes Ortiz" left Tijuana on Nov. 28 and was headed to the storage facility when it stopped to rest at a gas station in Tepojaco, in Hidalgo state north of Mexico City, driver Valentin Escamilla Ortiz told authorities.
He said he was sleeping in the truck when two men armed with a gun approached about 1:30 a.m. Tuesday. They made him get out, tied his hands and feet and left him in a vacant lot nearby.
When he was able to free himself, he ran back to the gas station to get help.
The truck has a GPS locator but it wasn't active at the time of the theft, Eibenschutz said.
Mexican customs officials are on alert, Eibenschutz said, to prevent the truck from crossing the border. He said the material could not be used to make a nuclear bomb, but could be used in a dirty bomb, a conventional explosive that disseminates radioactive material.
All of the U.S. ports of entry have radiation detectors in place, and trucks crossing the border are routinely screened for radiation.
There are an average of a half-dozen reported thefts of radioactive material in Mexico each year, Eibenschutz said, and none have proven to be intentional, meaning the thieves were not after the material. He said in all cases so far, they were after the containers or vehicles.
Such unintentional thefts are not uncommon, said an official familiar with cases reported by International Atomic Energy Agency member states, who was not authorized to comment on the case. In some cases, radioactive sources have ended up being sold as scrap, causing serious harm to people who unknowingly come into contact with it.
In a famous case in the 1970s of stolen radioactive material in Mexico, one thief died and the other was injured when they opened the container, he said. The container was junked and sold to a foundry, where it contaminated some of the steel reinforcement bar that was made there. Eibenschutz said all foundries in Mexico now have equipment to detect radioactive material.