A senior US official said on Thursday that satellite photographs of a suspected nuclear industrial site in Iran demonstrated its intention to develop atomic weapons, an allegation Tehran dismissed as "a new lie".
A prominent international expert said on Wednesday that new satellite images showed the Parchin military complex south-east of Tehran may be a site for research, testing and production of nuclear weapons. Iran denies having an atomic bomb programme.
"This clearly shows the intention to develop weapons," a senior US official told Reuters on condition of anonymity.
He also accused the UN nuclear watchdog of suppressing information on Parchin in its latest report on Iran - a charge denied by the International Atomic Energy Agency (IAEA).
A top Iranian official said the accusation that Tehran was hiding an atomic site from UN inspectors was a carefully timed lie intended to influence a resolution on its nuclear programme being discussed this week in Vienna by the IAEA governors.
"This is a new lie, like the last 13 lies based on news reports that have been proved to be lies," Hossein Mousavian, Iran's chief delegate to the IAEA board meeting told Reuters.
Washington and Tehran have been at daggers drawn since the 1979 Islamic revolution and the present US government says Iran's leadership is "evil" and set on developing nuclear arms.
David Albright, an American former weapons inspector who heads the Institute for Science and International Security think tank, made the allegation about Parchin on Wednesday. He also said the IAEA had asked to inspect Parchin but had been ignored.
Mousavian said: "They have not asked to see the site."
Asked if there had been a request on Parchin, IAEA spokesman Mark Gwozdecky would say only that it was "discussing with the Iranian authorities ... dual-use equipment and materials".
He dismissed as "baseless" the suggestion by the US official that the IAEA had concealed information on Parchin.
The agency's chief, Mohamed ElBaradei, said this week he was not convinced Iran's activities were entirely peaceful but that there was no hard evidence to prove the US belief Tehran was using its nuclear power programme as a front to build weapons.
Western intelligence agencies have recognised Parchin as a potential chemical, explosives and munitions production site since the 1990s. In November 2003, a Tehran parliamentarian complained publicly about spending on atomic technology and identified Parchin as a site for such activity.
France, Britain and Germany are in a sixth round of talks with IAEA board hardliners - the United States, Australia and Canada - to find a compromise on the wording of a text on Iran. The Europeans favour more negotiations with Tehran.
Negotiators from the six states were close to an agreement in private talks on Thursday and indicated they might have a final text of a resolution that could be adopted on Friday.
The most contentious of the US-backed proposals is for an "automatic trigger" leading to Iran being reported to the Security Council for possible economic sanctions if it does not stop its uranium enrichment programme by October 31.