The U.N. nuclear agency says a truck carrying an extremely dangerous radioactive substance has been stolen in Mexico.

The International Atomic Energy Agency says the truck was carrying cobalt-60, used for radiotherapy treatment to combat cancer. An IAEA statement Wednesday said the truck was stolen Monday while taking the material to a radioactive waste storage center from the northern city of Tijuana.

It says the heist occurred in Tepojaco, a town near Mexico City, and describes the load as “extremely dangerous” if damaged or removed from its protective shielding.

The statement says that Mexican authorities are searching for the material.