Vienna:
The US and Russia clashed at a UN atomic agency meeting Monday over Moscow's request for an IAEA probe into the risk of US airstrikes on Syria hitting a small reactor.
The head of the International Atomic Energy Agency, Yukiya Amano, said meanwhile that there was "not a big amount" of radioactive material at the research reactor in the suburbs of Damascus.
The US ambassador to the IAEA told a closed-door meeting of the watchdog in Vienna that carrying out Russia's request, made last week, was not the UN agency's job.
Joseph Macmanus said that "requests for comprehensive risk analyses of hypothetical scenarios are beyond the IAEA's statutory authority," according to a text of his remarks obtained by AFP.
"The IAEA has never before conducted this type of analysis, it would exceed IAEA's mandate, has far-reaching implications that exceed IAEA capabilities and authorities," he said.
While not mentioning Syria by name, he said the agency "will have to review such a request in light of legal authorities, mandate, and resources and must determine whether there is a scientific basis for conducting a highly speculative investigation of this kind."
Permanent UN Security Council member Russia opposes US-led airstrikes in response to an alleged use of chemical weapons by the regime of President Bashar al-Assad on August 21.
Last week Russia warned that US strikes could have "catastrophic" consequences if the reactor were hit, and has asked the IAEA to conduct a risk analysis.
Amano said on Monday the IAEA was "considering the request" and that the agency had to examine a number of legal, technical and political aspects before responding, telling reporters it was "a complicated issue".
He said however that the reactor contained around one kilo (two pounds) of highly-enriched uranium, saying that this was "not a big amount". He declined to comment however on the possible implications of a military strike.
He added that initial reactions from IAEA member states to Russia's request were "divided".