A senior Syrian official on Friday all but ruled out new visits by UN inspectors probing allegations that his country had a covert program that could be used to make nuclear weapons.
Syrian refusal to allow inspections could doom the International Atomic Energy Agency's efforts to follow up US assertions that a site reportedly bombed by Israel last year was a nearly finished reactor that could have produced plutonium.
Syria allowed the IAEA to visit the site near the desert town of Al Kibar in June but has since turned down requests for more inspections.
"We will not allow another visit," said Ibrahim Othman, the head of Syria's atomic agency.
He said the IAEA had agreed with Syria that there would be only be one visit. The IAEA has said it agreed to make one initial visit, but has requested others.
The IAEA has said it suspects three other sites may have been nuclear-related and linked to the bombed location.
Othman described the three sites as (non-nuclear) "military bases" that could not be visited by outsiders, although higher Syrian authorities could decide otherwise.
An IAEA report this week heightened concerns about Al Kibar, saying that satellite imagery and other evidence showed it had the characteristics of a nuclear reactor. It also said that soil samples taken from the bombed site had a "significant number" of chemically processed natural uranium particles.
A senior UN official, who demanded anonymity because the information was restricted, said the findings were unusual for a facility that Syria alleges had no nuclear purpose, but Othman dismissed the findings.
"Collecting three (uranium) particles from the desert doesn't mean there is a reactor there," he told reporters on the sidelines of an IAEA meeting on Syria and Iran.
Gregory L. Schulte, the chief US delegate to the IAEA, said the IAEA report reinforced suspicions "that Syria was secretly building a nuclear reactor." The US has said it believes Syria was working on the reactor with North Korean help.
Iran, meanwhile, heaped scorn on US allegations that Tehran's advances in uranium enrichment was moving it closer to nuclear arms capability, saying US President George W. Bush was "dreaming" of any excuse to give Washington an excuse to provoke confrontation. The US has not ruled out military action unless Iran stops enrichment and heeds other UN Security Council demands.
For years, Iran has been the focus of international concerns that it might seek to develop nuclear arms. It has been under IAEA investigation since 2002 - and UN sanctions since 2006 - due to revelations of covert atomic activities, allegations that it had past plans to develop such weapons and its refusal to stop enrichment, which can produce both reactor fuel and fissile warhead material.
Schulte said Iran's defiance of the UN Security Council ban on enrichment is "deeply troubling because it is only a small step from the low enriched uranium that Iran is now stockpiling to the highly enriched uranium that Iran would need to build a bomb."
Ali Ashgar Soltanieh, its chief IAEA delegate, dismissed Schulte's allegations.
"Bush many times was dreaming I am sure" that Tehran would kick out IAEA inspectors and break out of the Nonproliferation Treaty as an excuse for confrontation, said Soltanieh - adding that was something his country would not do.