The world's nuclear watchdog, the International Atomic Energy Agency (IAEA), conducted a second inspection of a Syrian reactor on Tuesday - a day after the agency made clear it was not satisfied with Syria's explanation about uranium particles found there.
The IAEA is trying to find out whether the country has a covert nuclear programme, and whether a site in the desert bombed by Israel in 2007 was really a secret nuclear facility.
Syria operates a small scientific reactor in Damascus that is being monitored by the Vienna-based nuclear agency. The organisation's inspectors have found and analysed traces of man-made uranium there.
IAEA chief Mohamed ElBaradei said in a report Monday that "the results do not support Syria's earlier explanation for the origin and presence of the particles".
The report struck a different tone than the previous one in August, when Syria was portrayed as being cooperative with regard to the Damascus reactor.
Informed about the IAEA's laboratory tests, Syria no longer claims that the uranium came to the reactor through contaminated equipment and now says the traces are connected to experiments and imported material that the IAEA had not been informed about.
While IAEA inspectors were able to visit the Damascus site, they have so far been prevented from examining the rubble of the bombed site, where a bigger reactor was allegedly being constructed.