By Bethany Bell
BBC News, Vienna
Syria says the al-Kibar site was a disused military building
The UN nuclear watchdog, the IAEA, says traces of undeclared man-made uranium have been found at a second site in Syria, at a reactor in Damascus.
The IAEA is investigating US claims that a Syrian site destroyed in a 2007 Israeli raid was a nuclear reactor that was not yet operational.
Separately, the agency says Iran is continuing to enrich uranium in defiance of the UN Security Council.
Both Iran and Syria deny allegations of illicit nuclear activities.
Last year, the IAEA (International Atomic Energy Agency) found particles of man-made uranium at the al-Kibar site in Syria, which was destroyed by Israeli missiles in September 2007.
Now in a confidential report obtained by the BBC, it says it has discovered new traces of uranium of a type not included in Syria's declared nuclear material.
The traces were found at a small reactor used for teaching in Damascus.
The IAEA says it is not clear whether there is a link between the particles found at the two sites.
In a separate report, the IAEA says Iran now has about 7,000 centrifuges - the machines used for enriching uranium. The agency says that Tehran is running almost 5,000 of them.
It also says that Iran has boosted its stockpile of low-enriched uranium (LEU) by 500kg to more than 1,300kg in the last six months.
David Albright of the Washington-based Institute for Science and International Security think-tank has said that Iran now had enough LEU to convert into high-enriched uranium (HEU) to make one atomic bomb.
However, he said Iran would need to overcome some technical hurdles to achieve this - a process that could take several years or more.
A senior official close to the IAEA says the agency has made little progress in its investigations in Iran and in Syria.
The agency has urged both countries to co-operate with its inspectors.