A police agent stands guard as an ambulance leaves the village of Hueypoxtla, Mexico, Wednesday, Dec. 4, 2013. Mexican troops and federal police kept a nighttime vigil guarding a rural field where thieves abandoned a stolen shipment of highly radioactive cobalt-60, while officials began planning the delicate task of safely recovering the dangerous material. The cargo truck hauling the cobalt-60 was stolen from a gas station Tuesday in the neighboring state of Hidalgo, about 40 kilometers (24 miles) from where the material was recovered. (AP Photo/Marco Ugarte)

MEXICO CITY - Mexican troops and federal police kept a nighttime watch on a rural field where thieves abandoned a stolen shipment of highly radioactive cobalt-60, while officials began planning the delicate task of recovering the dangerous material.

Juan Eibenschutz, director general of the National Commission of Nuclear Safety and Safeguards, said late Wednesday that it could take at least two days to safely get the material into a secure container and transport it to a waste site.

"It's a very delicate operation," Eibenschutz said. "What's important is that the material has been located and the place is being watched to guarantee no one gets close."

The missing shipment of radioactive cobalt-60 was found Wednesday near where the stolen truck transporting the material was abandoned in central Mexico.

The highly radioactive material had been removed from its container, officials said, and one predicted that anyone involved in opening the box could be in grave danger of dying within days.

The cobalt-60 was left in a rural area about a kilometre (a half a mile) from Hueypoxtla, a farm town of about 4,000 people, but it posed no threat to the residents and there was no evacuation, Eibenschutz said.

"Fortunately there are no people where the source of radioactivity is," Eibenschutz said.

Townspeople complained they hadn't been given any information about what had been found in the nearby field.

"We don't know anything," resident Jose Antonio Rosales told Milenio Television. "We don't know if it's good, if it's bad. The authorities haven't told us anything."

Federal police and military units on the scene threw up an armed cordon about 500 metres (yards) around the site.

Mardonio Jimenez, a physicist for the nuclear commission, said it was the first time cobalt-60 had been stolen and extracted from its container in Mexico. The only threat was to whoever opened the box and later discarded the pellets of high-intensity radioactive material inside, he said.

"The person or people who took this out are in very great risk of dying," Jimenez said, adding that the normal survival rate would be between one and three days.

He said there was no word so far of anyone reporting to area hospitals with radiation exposure. He said those who exposed themselves to the pellets could not contaminate others.

The cargo truck hauling the cobalt-60 was stolen from a gas station early Monday in the neighbouring state of Hidalgo, about 40 kilometres (24 miles) from where the material was recovered, Jimenez said. Authorities had put out an alert in six central states and the capital looking for it.

The material had been removed from obsolete radiation therapy equipment at a hospital in the northern city of Tijuana and was being transported to nuclear waste facility in the state of Mexico, which borders Mexico City.

Eibenschutz said there was nothing to indicate the thieves were after the cobalt or in any way intended for an act of terrorism, The thieves most likely wanted the white 2007 Volkswagen cargo vehicle with a movable platform and crane , he said.

On average, a half dozen thefts of radioactive materials are reported in Mexico each year and none have proven to be aimed at the cargo itself, he said.

According to authorities, a truck marked "Transportes Ortiz" left Tijuana on Nov. 28 and was headed to the storage facility when the driver stopped to rest at a gas station in Tepojaco, in Hidalgo state north of Mexico City.

The driver told authorities he was sleeping in the truck when two men with a gun approached him. They made him get out, tied his hands and feet and left him in a vacant lot nearby.

Eibenschutz said the transport company did not follow proper procedures and should have had GPS and security with the truck.

"The driver also lacked common sense because he decided to park along a highway so he could sleep," he said.

The company that owns the truck couldn't immediately be located for comment. One Mexico City company called "Transportes Ortiz" said the truck was not theirs and they had nothing to do with the incident.

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Associated Press writers Emilio Lopez in Pachuca and Katherine Corcoran, E. Eduardo Castillo and Adriana Gomez Licon in Mexico City contributed to this report.

News from © The Associated Press, 2013