The Beijing Olympics could be threatened by terrorists who are trying to obtain nuclear materials in the run-up to the games, the United Nations nuclear watchdog warned today.

Terrorists may use so-called “dirty bombs” to disperse radioactive materials at the event, the International Atomic Energy Authority said as it staged its biggest ever security training exercise in the Chinese capital.

The watchdog told the BBC that the same threats will exist for the London Games in 2012 when a massive security operation will be put in place.

The IAEA said there is no specific information an imminent attack on the Beijing games, but intelligence shows terrorists are trying to obtain nuclear materials.

The possibility that terrorists will use dirty bombs that use conventional explosives to disperse radioactive material is under investigation.

Dirty bombs are not normally associated with high death tolls, but the spread of nuclear material can cause fear and alarm and exposure to dangerous levels of radiation.

During the training and simulation exercise, the IAEA said the same threats would exist in London for the 2012 Games, where organisers are working to ensure a safe and secure event.

An IAEA spokesman said: “We are providing them with assistance with nuclear security, which is par for the course in any big sporting or public event such as this.

“We provide assistance for member states when it is requested.”