The director of the UN atomic watchdog, has said a report he is due to present later this week on Syrian nuclear activity will "not be conclusive".
"We still have work to do," the head of the International Atomic Energy Agency, Mohamed ElBaradei, said in Dubai.
"We need more co-operation from Syria... We need also co-operation from Israel," Mr ElBaradei told reporters.
Recent unconfirmed reports said the IAEA had found traces of atomic material on a site bombed by Israel.
"We won't be able to reach a quick conclusion unless we have credible information.
"There was uranium but it doesn't mean there was a reactor... It's not highly enriched uranium," Mr ElBaradei added.
The US has said the target of Israel's raid in September 2007 was a secret nuclear reactor built with North Korean help that was nearing completion.
Syrian officials said the site was a disused military building and accused US intelligence agencies of fabricating evidence against their country.
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.
Syria's Foreign Minister Walid Muallim dismissed as politically motivated last week's press disclosures, attributed to unnamed diplomats linked to the UN watchdog.
He said uranium could have come from munitions used by Israel to bomb the site.
Damascus had said it will co-operate with the IAEA inquiry only if it does not threaten its national security