A truck containing potentially "extremely dangerous" radioactive material has been stolen in Mexico's northern city of Tijuana, the UN atomic watchdog said.

The International Atomic Energy Agency said on Wednesday that the vehicle was transporting a cobalt-60 from a hospital from a hospital to a radioactive waste storage centre when it was stolen.

"The Mexican authorities are currently conducting a search for the source and have issued a press release to alert the public," the IAEA said in a statement.

The material could not be used in a conventional nuclear weapon but could in theory be put in a so-called "dirty bomb" - an explosive device spreading the radioactive material over a wide area.

Experts have long warned about the danger posed by the large amounts of such material held in hospitals and other locations around the world under insufficient security.

The Agency was informed about the December 2 theft by Mexico's CNSNS nuclear security authority, the IAEA said.

Similar incidents

Last year alone, the IAEA recorded 17 cases of illegal possession and attempts to sell nuclear materials and 24 incidents of theft or loss. It says this is the "tip of the iceberg".

Many cases have involved former parts of the Soviet Union, such as Chechnya, Georgia and Moldova - where in 2011 several people were arrested trying to sell weapons-grade uranium - but not only.

Major international efforts have been made since the demise of the Soviet Union in 1991 and the September 11, 2001 attacks in the United States to prevent nuclear material falling into the wrong hands.

US President Barack Obama hosted a summit in 2010 on the subject which was followed by another one in Seoul last year. A third is planned in The Hague in March 2014.

A report issued in July by the Arms Control Association and the Partnership for Global Security said decent progress had been made reducing the threat but that "significant" work remained.