Syria has blocked further visits by UN nuclear inspectors
The UN nuclear agency says it has found additional particles of uranium in samples taken from the site of an alleged nuclear facility in Syria.
Syria denied the site was a nuclear reactor and alleged the uranium traces found there came from Israeli missiles fired on it in September 2007.
But the International Atomic Energy Agency said the probability of the uranium coming from missiles was low.
The IAEA called on Syria to co-operate more with its inquiry.
It said Syria had not answered many of the agency's questions about the destroyed facility.
Israeli warplanes flattened the facility in the Syrian desert in 2007 on suspicion that it was part of a covert nuclear weapons programme.
The report for the IAEA board members has been seen by news agencies ahead of a meeting to discuss Syria next week.
It said IAEA inspectors had been blocked from making follow-up visits to the site.
The latest report comes after a November report said the site had features resembling those of a nuclear reactor site, but it did not exclude the possibility that it was being used for purposes unrelated to nuclear activity.
In that first report on its findings, the IAEA said "significant" traces of uranium were also found.
Syria has always maintained the site was a disused military building.
The IAEA also reported on Thursday that Iran has slowed the expansion of its uranium enrichment plant but had built up its stockpile of nuclear fuel.
The agency said Iran had only slightly increased the number of centrifuges refining uranium - a process that can produce fuel for civilian energy or atomic weapons.
But Iran's reported stockpile of low-enriched uranium had risen to 1,010kg.
Unnamed IAEA officials briefed journalists that this amount of uranium was sufficient, with added purification, to make an atom bomb.
Iran insists its nuclear programme is for civilian purposes only. Iran's continued enrichment of uranium is in defiance of UN Security Council resolutions.