The UN says it is not aware of any specific threat to the Olympics
The UN's nuclear watchdog says it is training Chinese security officials to deal with a possible radiological attack during the Olympics Games.
Nuclear experts have staged simulated exercises with Chinese officials, although the watchdog said it was unaware of any specific threat.
Drills included what to do if a so-called "dirty bomb" was smuggled into an Olympic venue in Beijing.
The games are due to be held in the Chinese capital from 8-24 August.
"The awareness after the 9/11 attacks [was] that there are basically no limits for what can be done," said Anita Nilsson, of the International Atomic Energy Agency's (IAEA) Office of Nuclear Security.
"In this case it is better to be proactive, to review the practices and to put them up to standard and to implement them," she said.
IAEA and Chinese officials have carried out a series of simulated exercises in Beijing, including how to respond to the discovery of a suspected "dirty bomb" in a restaurant.
A "dirty bomb" is a weapon designed to contaminate the local environment by disbursing radioactive material.
Peter Colgan, one of Dr Nilsson's deputies, said the exercises had gone "very well".
Dr Nilsson warned that the same threats would exist for the London Olympics in 2012.
"There is a major shift in threat perception over the last five to 10 years. And we have to take that into account and to do accordingly, whether it is Olympic games in Beijing or London. These measures must be implemented."
Organisers of the 2012 games say "work is progressing to ensure a safe and secure" event.