The International Atomic Energy Agency says it has found processed uranium particles at a nuclear site in Syria, which raise questions of the country’s possible development of nuclear weapons.

A random test at a small research reactor in Damascus found processed uranium particles not included in Syria’s declared inventory of nuclear material.

The agency said in a report that the presence and origin of such particles needed an explanation from the country concerned.

UN officials said that it was extremely unlikely that the traces were a result of Israel’s attack on the site in 2007, as reasoned by Syria.