VIENNA (Reuters) -- UN inspectors have revisited a Damascus nuclear-research reactor to take more swipe samples after judging Syria's initial explanation for uranium traces found there to be doubtful.
An International Atomic Energy Agency (IAEA) official confirmed inspectors were at the site a day after an IAEA report said tests of samples taken in August 2008 showed the traces did not come from Syria's declared nuclear inventory, as it maintained.
The report also said Syria was still blocking follow-up IAEA access to a desert site of what U.S. intelligence reports said was a nascent, North Korean-designed nuclear reactor geared to yield atomic bomb fuel, before Israel bombed it in 2007.
The Vienna-based IAEA has been checking whether there could be a link between the Damascus and Dair Alzour sites since discovering mysterious particles of processed uranium at both.
Some analysts have said the findings raised the question of whether Syria used some natural uranium intended for the alleged reactor at Dair Alzour in tests applicable to learning how to separate out bomb-grade plutonium from spent nuclear fuel.
Syria, an ally of Iran which is under IAEA investigation over nuclear proliferation suspicions, has denied ever having an atom bomb program and has said the intelligence is fabricated.
Syria told the IAEA earlier this month that the traces at the Damascus site could have come from domestically-produced uranium concentrate known as "yellow cake", or from imports of commercial uranyl nitrate which it had not declared to the IAEA.
The November 17 inspector trip aimed to verify that assertion.
Syria at first told the IAEA that the traces found last year came with contaminated equipment used at the site, but IAEA test results did not stand up this explanation, and the particles could not be traced to Syria's declared inventory.
"They have [now] acknowledged doing experiments with natural uranium compounds, some originating from yellowcake which they have got from their own facility or laboratory," a senior official close to the IAEA said.
IAEA inspectors examined the desert Dair Alzour site in June 2008 but Syria has barred renewed access and also not let them visit three military sites, whose appearance was altered by landscaping after the IAEA first asked to check them.
"No progress has been made since the last report to clarify any of the outstanding issues," the November 16 agency report said.