Iran announced Monday that it had launched a trial run at a uranium enrichment factory in Natanz, at the centre of Western concerns over its nuclear programme.
"This was expected to happen. It was not desired. It is not the best answer to what we have requested," a Western diplomat close to the UN nuclear watchdog, the Vienna-based International Atomic Energy Agency (IAEA) told AFP.
He said it showed that Iran "might be restricted in their cooperation."
The IAEA's board of governors had on September 12 given Iran until October 31 to suspend its uranium enirchment activities and to provide information on traces of highly enriched uranium that could be weapons-grade found at Natanz by IAEA inspectors.
The Iranians have said that the uranium traces were the result of second-hand equipment imported into the country and that Natanz is enriching uranium for use in a reactor it is building to produce nuclear energy.
The United States charges the uranium could in fact be enriched more than is needed for civilian use, to levels needed to make atomic weapons.
"We were aware in June that Iran had started test operations at the plant at Natanz and our report to the (IAEA) board in August reflected that fact," IAEA spokesman Mark Gwozdecky said.
A Western diplomat said the Iranians continuing enrichment operations at Natanz could make it impossible to prove where the highly enriched uranium had come from.
Iran fiercely denies it is seeking to acquire nuclear weapons, but its failure to comply with the IAEA deadline could lead to Tehran being declared in non-compliance with the nuclear Non-Proliferation Treaty, with the matter being passed to the UN Security Council.