Authorities arrested six people on suspicion of involvement in this week's theft of a truck carrying nuclear material, a source in the Mexican Attorney General's Office told Efe Friday.

The suspects were taken under guard to the General Hospital in Pachuca, capital of the central state of Hidalgo, for tests to determine whether they suffered exposure to radiation, the source said.

They were apprehended in Pachuca in the course of the investigation into the robbery.

The truck was stolen on Monday in Tepojaco, Hidalgo, while transporting cobalt-60 from a hospital in the northern border city of Tijuana to a radioactive waste storage center.

Once the medical examinations are complete, the suspects will be taken to Mexico City for questioning, the source in the AG's office said.

But the press secretary for the Hidalgo state Health Department told Efe that the six individuals showed no signs of radiation exposure and had been cleared for release.

The six remain inside the hospital and "the rest is up to the AG's office," Yadira Martinez said.

Mexican authorities located the truck and the radioactive material Wednesday afternoon near the town of Hueypoxtla, Mexico state, not far from where the vehicle was stolen.

While the cobalt-60 had been removed from its protective shielding, technicians from Mexico's nuclear agency found no trace of radioactive contamination in the area.

Anyone touching or coming into close contact with the unshielded cobalt-60 for more than a few months would likely suffer permanent injury, the International Atomic Energy Agency said. EFE