Mexican authorities found Wednesday a stolen medical device containing dangerous radioactive material outside the truck that was carrying it north of Mexico City, threatening the lives of those who touched it, officials said.

Military and police forces cordoned off the area to prevent contamination after finding the radiation treatment machine in a rural area north of Mexico City two days after the truck was stolen.

The device containing cobalt-60 was taken out of its steel-reinforced wood container and left hundreds of meters (yards) from the truck in Hueypoxtla, said Mardonio Jimenez, operations director at the National Commission for Nuclear Safety and Safeguards (CNSNS).

"It's almost absolutely certain that whoever removed this material by hand is either already dead or about to die," CNSNS director Juan Eibenschutz told Milenio television.

Authorities said they did not need to evacuate the area because it was sparsely populated.

Eibenschutz said the transport company failed to live up to its commitment, saying the truck lacked a tracking device or proper security despite the firm's experience. He said the matter should be investigated.

The white Volkswagen Worker truck was transporting the device from a hospital in the northwestern city of Tijuana when it was stolen at a service station in central Hidalgo state on Monday.

The vehicle was supposed to deliver the material to a radioactive waste disposal facility in the central state named Mexico.

The International Atomic Energy Agency warned that the material was "extremely dangerous" if removed from its shielding. Experts also said the 60 grams of cobalt-60 inside it was enough to make a "dirty bomb."

Authorities had searched for the truck in six states and the capital, delivering radio messages for people to call an emergency number in case they saw the truck.

The driver told investigators that two gunmen approached him at a Pemex service station, tied him up and drove away with the truck, according to a text of the testimony shown by the Hidalgo state prosecutor's office.

The manager of the Pemex service station, an hour's drive north of Mexico City, told Agence France Presse the driver appeared to have parked across the street to rest overnight.

The material was on its way to the Radioactive Waste Storage Center in Maquixco, Mexico state. The facility is surrounded by a white fence topped with barbed wire, but no armed guards were visible outside, an AFP correspondent said.

An official from the center said the truck driver had been waiting for the facility to open at 8:00 am on Tuesday.

Mexico's drug cartels have diversified their illegal activities in recent years, stealing oil and minerals, but officials have not said who the cobalt-60 thieves might be.

'Sufficient' for dirty bomb

Experts have long warned about the risks posed by the large amounts of radioactive material held in hospitals, university campuses and factories, often with little or no security measures to prevent them being stolen.

In an incident involving a teletherapy device in Thailand in 2000, 425 Curies -- the measure of radioactivity -- of cobalt-60 was sufficient to make 10 people very ill, three of whom died, according to the IAEA.

The equipment stolen in Mexico contained nearly 3,000 Curies, CNSNS radiological security director Jaime Aguirre Gomez told AFP.

Cobalt-60 is a radioactive isotope of the metallic element cobalt and the gamma rays it emits destroy tumors, but contact or just being near it can cause cancer if not properly handled and sealed.

More worryingly, though, such material could in theory be put in a so-called "dirty bomb" -- an explosive device designed to spread the radioactive material over a wide area.

The quantity stolen in Mexico was "sufficient" to make a dirty bomb, said Michelle Cann, an analyst at the Partnership for Global Security.

"But the ultimate level of damage and contamination hinges on many factors," she said.