Authorities in Mexico, on Wednesday, recovered the truck which was carrying dangerous radioactive isotopes and was reported stolen near Mexico City. The radioactive material laden truck was found after two days of search.

New York Times quoted a safety official; Mardonio Jimenez of Mexico's nuclear safety commission, said authorities had recovered a box containing some of the isotope, cobalt 60, which was used for medical purposes along with the truck.

The whereabouts of the remaining cargo was, however, unclear, the report said.

News of the theft was publicised on Wednesday by the UN-backed, International Atomic Energy Agency (IAEA), raising concerns as cobalt 60 is extremely dangerous when exposed to humans.

Accordingly to the New York Times, the theft raised fears of a sinister motive to develop a "dirty bomb."

"The people who took that material are going to have to stop in the hospital and we will be waiting for them," Mr Jimenez is reported to have said in a televised interview.

Fox News reports that the truck marked "Transportes Ortiz" left the northern city of Tijuana on Nov. 28 carrying the isotope from a hospital to a radioactive waste storage facility. The truck was stolen when the driver stopped to rest at a gas station in Tepojaco, in Hidalgo state north of Mexico City.

The truck driver, Valentin Escamilla Ortiz, told authorities that he was sleeping inside the vehicle when two men armed with a gun approached him, asking him to get out, tied his hands and left him in a vacant lot before escaping with the truck and cargo. When the driver was able to free himself he ran to the gas station to get help.

Although the material was properly shielded from exposure at the time of the theft, the IAEA said, "the source could be extremely dangerous to a person if removed from the shielding or if it was damaged."

The New York Times quoting a U.S. military official said Pentagon was monitoring the Mexico situation closely although the theft did not appear to be connected to any terrorist activity.

"I would say we are concerned but not worried," the newspaper quoted the military official who wished to be anonymous, as saying.

"No indication at all this was terror related - just simple vehicle theft. It was used medical-grade material on its way to a disposal site, so would have already decayed to the point that it would not be useful for a weapon even if it did fall into terrorist hands," the official said.

Fox News, meanwhile quoted Mexico's director general of the National Commission of Nuclear Safety and Safeguards, Juan Eibenschutz saying that on an average, half a dozen thefts of radioactive materials are reported in Mexico each year, although, none have proven to be aimed at the cargo.

In all the cases the thieves were after shipping containers or the vehicles, Mr Eibenschutz said.