Syria said it was co-operating fully with a UN inquiry into allegations of secret nuclear work in the country but would not go as far as opening up military sites because this would undermine its security.

The Vienna-based UN nuclear watchdog has been probing Syria since May over US intelligence allegations that it was close to completing a secret, plutonium-producing reactor before Israel flattened the site in an air strike a year ago.

Syria has denied having a clandestine nuclear program. It does have one declared nuclear site - a research reactor.

The IAEA said last week that preliminary findings from test samples taken by inspectors granted a visit to the desert location in June bore no traces of atomic activity. Syria says all that was there was a disused military building.

“We would like to underline that my government is co-operating with the agency in full transparency and will follow suit all along the way,” said Ibrahim Othman, director-general of Syria's Atomic Energy Commission.

“However, this cooperation will not in any way come at the expense of exposing our military sites or causing a threat to our national security,” he told the annual meeting of the IAEA's 145-nation General Conference, or assembly, in Vienna.

Diplomats close to the IAEA have said Syria has ignored agency requests to check three military installations believed connected to the alleged reactor site.