Syria says the site was a disused military building
A Syrian site bombed by Israel last year had features resembling those of a nuclear reactor site, the UN nuclear watchdog says in a report.
But the International Atomic Energy Agency did not exclude the possibility the site was being used for purposes unrelated to nuclear activity.
In the first report on its findings in Syria, the IAEA said "significant" traces of uranium were also found.
Syria has always maintained the site was a disused military building.
Israeli warplanes flattened the facility in the Syrian desert in September 2007 on suspicion that it was part of a covert nuclear weapons programme.
"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," said the IAEA report, sent to its 35-nation board of governors ahead of a meeting next week.
It added that IAEA inspectors had found "a significant number of natural uranium particles" in environmental samples taken from the site.
IAEA inspectors visited the bombed al-Kibar site in June, where they took samples that appear to have contained the radioactive material, but Damascus has blocked any follow-up trips.
According to the confidential report, a copy of which was obtained by the BBC, Syria says the uranium found there was residue from the Israeli missiles used in the air-raid.
The IAEA says it wants to visit three locations in Syria to take further samples.
It also says it will ask Israel to provide information about Syria's claims about the uranium particles.
But a senior official close to the IAEA said the type of uranium found was not that usually found in munitions.
IAEA head Mohamed ElBaradei has called on Syria to show transparency and allow his inspectors access to the necessary sites and information.
Mr ElBaradei said the IAEA's investigation had been severely hampered both by Israel's use of force and by a US failure to hand over intelligence until seven months after the bombing.
The agency's investigation had also been made more difficult by the fact that Syria has erected a new building on the bombed out site.
The IAEA also noted that Syria had not produced requested documentation to support its declarations about the nature of the building.
The US has said the target of Israel's raid was a secret nuclear reactor built with North Korean help that was nearing completion.