"If the Americans have any claims or information, they should hand it over to the (UN nuclear watchdog) agency, but it's clear they have nothing," said Hasan Rohani, the Supreme National Security Council's secretary general, in Tehran on Wednesday.
He said the International Atomic Energy Agency (IAEA) had only minor concerns about Iran and would soon be able to reassure the world Tehran has no atomic arms ambitions.
IAEA chief Muhammad ElBaradei told NATO parliamentarians on Tuesday, however, that he could not rule out that Iran's nuclear programme was linked to a military weapons programme.
The IAEA said on Tuesday in a confidential report on Iran there are two major issues it must resolve.
The first is the origin of enriched uranium traces found at sites in Iran. The second is Iran's centrifuge programme, especially its interest in advanced P2 enrichment centrifuges capable of making bomb-grade uranium.
Hasan Rowhani urges the US to
provide proof for its accusations
The report said Iran had admitted importing P2 parts and may have had interest in parts for thousands of centrifuges - contrary to what it told the agency before.
The United States accuses Iran of running a secret nuclear-weapons programme that is parallel to its declared atomic energy programme.
Iran denies this, insisting its ambitions are limited to the peaceful generation of electricity.
"I think the administration oversteps the evidence by saying it knows Iran has a weapons programme," said David Albright, a former UN weapons inspector and president of the Institute for Science and International Security in Washington.
"There's no evidence that's been found that shows they have an active nuclear-weapons programme," Albright said.