US summons Syrian ambassador over nuclear issue

US officials have summoned Damascus' ambassador in Washington after the UN nuclear watchdog found unexplained uranium particles at a desert site in Syria, a State Department spokesman has said.

Spokesman Gordon Duguid on Friday said US officials have asked to meet with Syria's ambassador Imad Moustapha "to discuss our concerns."

There remain "key differences between our two governments including concerns about Syrian support to terrorist groups and networks and Syria's pursuit of non-conventional nuclear weapons," he added.

On Thursday, Washington urged the International Atomic Energy Agency to discuss what it said was mounting evidence of a clandestine nuclear program in Syria at a meeting next month in Vienna.

In a report, the IAEA rejected assertions by Damascus that particles of uranium found at the remote desert Al-Kibar site came from Israeli missiles used to bomb it in September 2007.

"It's nuclear material that hasn't been declared and Syria has to explain" how it got there, said a senior IAEA official, speaking on condition of anonymity.