Thieves have made off with a truck in Mexico carrying a dangerous radioactive source used in medical treatments, a material that could also provide an ingredient for a so-called "dirty bomb".

The UN nuclear agency said it had been informed by Mexican authorities that the truck, which was taking cobalt-60 from a hospital in the northern city of Tijuana to a radioactive waste-storage centre, was stolen near Mexico City on Monday.

An image provided by Mexico's CNSNS safety authority of a container carrying medical equipment with a radioactive source, which was in a white Volkswagen truck that was stolen on Monday. Credit:AFP Photo

Apart from peaceful medical and industrial uses, experts say cobalt-60 can also be used in a dirty bomb in which conventional explosives disperse radiation from a radioactive source.

The International Atomic Energy Agency, which has stepped up calls on member states to tighten security to stop nuclear and radioactive materials falling into the wrong hands, made no mention of any such risk in its statement on Wednesday.