UN inspectors have found enriched uranium in environmental samples taken in Iran, which could mean Tehran has been enriching uranium without informing the UN nuclear watchdog, diplomats said.
The diplomats, who asked not to be named, said initial analysis showed enrichment levels possibly consistent with an attempt to make weapons-grade material and high enough to cause concern at the International Atomic Energy Agency (IAEA).
Iran said later on Friday the IAEA had not told it about any findings.
"The International Atomic Energy Agency has not told Iran about this issue," Khalil Mousavi, spokesman for Iran's Atomic Energy Organization, said. "As soon as the agency takes a stance on this, then we will announce our stance," he said.
If Iran, dubbed part of an "axis of evil" by Washington, has enriched uranium without telling the IAEA, it would deepen US suspicions that Tehran's nuclear ambitions go beyond its stated aim of using nuclear energy to generate electricity.
Without confirming that UN inspectors had found enriched uranium, US State Department spokesman Richard Boucher said: "I think this substantiates those statements that we've made over time" and said Washington wanted the IAEA to provide more information before its next report is due on Sept. 8.
However, the diplomats said the mere presence of enriched uranium in the samples was not solid proof Iran had done the enrichment itself. Contamination was another possibility, though how it had arisen would have to be explained to the IAEA.
The head of the IAEA declined to comment to reporters on the statements of the diplomats about the samples.
"Any media reporting on sample results would be pure speculation," IAEA chief Mohamed ElBaradei said after a board of governors meeting on the agency's budget.
IAEA spokeswoman Melissa Fleming said that the initial results were being reviewed at the agency and they expected to take more samples over the next few weeks.
"Only the IAEA will be in a position to judge the significance of the analysis results," Fleming said. "At this point, we are still in the middle of a complex inspection process in Iran, in which we are investigating a number of unresolved issues."
Iran insists it has no interest in building nuclear weapons, as Washington charges, but has resisted calls for it to accept tougher inspections of its nuclear program.
It was not clear at which of Iran's nuclear facilities the samples had been taken.
Last month, the IAEA's board of governors chided Iran for failing to report many aspects of its nuclear program and asked for more information on research and development in Iran's uranium enrichment program.
ElBaradei told the IAEA board he hoped Iran would accept the tighter inspection regime to provide assurances that its nuclear program is peaceful.
At least one senior Western diplomat predicted last month that environmental samples taken by the IAEA would confirm suspicions that Iran continues to hide aspects of its nuclear program -- including live tests of enrichment centrifuges.
Iran has repeatedly denied that it has tested its centrifuges with nuclear material without telling the IAEA.
But diplomats say it makes no sense for Iran to spend hundreds of millions of dollars to build big uranium enrichment facilities in Natanz without having tested their centrifuges.