U.S.-Russian tensions over Syria spilled into a U.N. nuclear watchdog meeting on Monday when the two clashed over whether inspectors should analyze possible risks involved if a reactor near Damascus were to be hit during U.S.-led strikes.
Russia said last week any military action against Syria's government could have catastrophic effects if a research reactor near the Syrian capital that contains radioactive uranium was struck "by design or by chance".
Russia's Foreign Ministry called on the International Atomic Energy Agency (IAEA) to urgently assess the issue with the United States preparing for punitive strikes in Syria over an alleged poison gas attack in its civil war.
But in a statement to an IAEA board of governors meeting on Monday, where Moscow reiterated its demand, U.S. Ambassador Joseph Macmanus made Washington's objections clear.
"It is our view that requests for comprehensive risk analyses of hypothetical scenarios are beyond the IAEA's statutory authority," he said, according to a copy of his speech in the closed-door session.
The IAEA "must determine whether there is a scientific basis for conducting a highly speculative investigation of this kind," Macmanus added.
Moscow is the Syrian government's most powerful ally and main arms supplier and has blocked U.N. Security Council action sought by Western powers to stop Syria's war and bring about a political transition. The West has backed the two-and-a-half-year old uprising against Syrian President Bashar al-Assad.
IAEA Director General Yukiya Amano said the U.N. agency was considering the Russian request, describing it as a "complicated issue" with technical, political as well as legal aspects.
Russia had asked for a quick response but "I hope people understand that it takes time," Amano told a news conference.
"The views are divided so far," he said about statements made on the issue by Russia, the United States and Cuba during the board meeting, which is due to end on Friday and will also debate Iran and other topical nuclear matters.
NO "BIG AMOUNT" OF HEU
Amano said the Syrian reactor - which IAEA inspectors have visited in the past - holds about 1 kg (2.2 pounds) of highly-enriched uranium (HEU), saying this was not a "big amount".
He said Syria as far as he knew only had one research reactor but he suggested that hospitals and research institutes may also have radioactive sources, without elaborating.
Nuclear experts say the so-called Miniature Neutron Source Reactor (MNSR), a type of research reactor that is usually fuelled by HEU, is small but that any radioactive fallout might pose a local hazard.
The kilogram of HEU that such a reactor usually holds is only a small fraction of the 25 kg (55 pounds) that would be sufficient to assemble a single nuclear bomb, they say.
Olli Heinonen, a former chief IAEA inspector, said other radioactive materials may be a bigger reason to worry.
"Syria should have substantial amounts of radiation sources such as Co-60 or Cs-137, which in my view are of a greater concern, if they end up in wrong hands. Normally they are stored in protected vaults," he told Reuters in an e-mail.
Russia said nearby areas could be contaminated by highly enriched uranium and that it would be impossible to account for the nuclear material after an air strike, suggesting it could fall into the hands of people who might use it as a weapon.
In a letter to other member states seen by Reuters, Russia said it had asked the IAEA to "react without further delay to the current situation and to provide member states with full analysis of risks associated with possible American strikes on MNSR and other sites in Syria".
But Macmanus, the U.S. envoy, said: "The IAEA has never before conducted this type of analysis. It would exceed the IAEA's mandate, (and) has far-reaching implications that exceed IAEA capabilities and authorities."