Nevertheless, puzzling anomalies had been found at the site, the International Atomic Energy Agency said.

"We are not in a situation to say that it was a nuclear reactor," an official close to the IAEA said, adding at the same time that "we cannot exclude that it was" one.

The watchdog addressed the matter in a restricted report circulated to the agency's board of governors on Wednesday, a copy of which was obtained by AFP.

"While it cannot be excluded that the building in question was intended for non-nuclear use, the features of the building ... along with the connectivity of the site to adequate pumping capacity of cooling water are similar to what may be found in connection with a reactor site," the IAEA said.

Furthermore, traces of uranium had been found by IAEA investigators in environmental samples taken from the site, known alternatively as either Al-Kibar or Dair Alzour, which was razed to the ground by Israeli planes on September 6, 2007.

"The analysis of these particles indicates that the uranium is anthropogenic. ie. that the material was produced as a result of chemical processing," the report said.

"No such nuclear material had so far been declared in Syria's inventory ... In principle, that sort of nuclear material should not exist there. It's not usual to find man-made uranium in sand," a senior UN official said.

The United States claims Dair Alzour was a nuclear facility built with North Korean help and close to becoming operational.

But Damascus has dismissed the allegations as "ridiculous" and said the site was a disused military facility.

Syria claims the traces of uranium found at the site were residue from Israeli missiles used to bomb the area.

The IAEA's inspectors had "not been able to establish the exact origin, because the particles were fairly small," the senior UN official said.

A second official said the report -- the IAEA's first since it dispatched a team of experts to investigate Dair Alzour in June -- was "not conclusive."

The IAEA was "assessing Syria's explanation of the origin of the uranium particles."

It added that it "intends to request Syria to permit the agency to, inter alia, visit the locations where the debris from the building and any equipment removed from the Dair Alzour site are, for the purpose of taking samples."

"The Agency also intends to request Israel to provide information pertaining to Syria's claims regarding the origin of the uranium particles."

IAEA Director General Mohamed ElBaradei urged Syria "to provide the necessary transparency," including permission for follow-up visits to Dair Alzour, plus visits -- so far denied -- to three other related locations "and access to all available information".

But he also called on "other states that may posess relevant information, including satellite imagery, to make this available to the agency and to authorise the agency to share the information with Syria."

ElBaradei complained that the IAEA's work had been "severely hampered ... by the unilateral use of force and by the late provision of information concerning the building at the Dair Alzour site."

"In light of the destruction of the building and the subsequent removal of the remains, the agency's verification of the situation has been made more difficult and complex, as well as more time and resource consuming," the report said.

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