Iran said on Wednesday that "no nuclear activity whatsoever" has taken place at its military site of Parchin, which UN nuclear watchdog inspectors demanded last week to visit but were refused.
"No nuclear activity whatsoever has taken place on the Parchin site," the head of Iran's Nuclear Energy Organisation, Fereydoon Abbasi Davani, was quoted by the official IRNA news agency as saying after a cabinet session.
"It is up to the country's military officials to decide any request by foreign nationals to visit Parchin," he added.
The International Atomic Energy Agency said last week it "continues to have serious concerns regarding possible military dimensions to Iran's nuclear programme" following an unsuccessful visit to Tehran by a five-strong inspection team.
The inspectors, who visited February 20-21, had asked to see the Parchin military base east of Tehran but Iranian officials rejected the request.
An IAEA report published in November said there was a "a large explosives containment vessel" at Parchin being used to test big amounts of conventional explosives consistent with designing a nuclear warhead for Iran's Shahab-3 ballistic missiles.
As a signatory to the Nuclear non-Proliferation Treaty (NPT) supervised by the IAEA, Iran has to submit to UN inspections at its declared nuclear sites.
But military sites that do not have confirmed nuclear activities are off-limits unless provided for by agreement or under the terms of an Additional Protocol to the NPT that Iran briefly adhered to but dropped in 2006.
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Abbasi Davani was quoted as saying: "There is no reason for us to give access to any geographical point in our country at the mere request of the (UN) agency."
The Iranian nuclear chief said he hoped that talks with the IAEA "will continue in the future."
But he said that, while "we have no problem to further explain our nuclear activities" to the IAEA, "we need to consider our rights and national interests."
He notably dismissed imposing any "set timeframe" on Iran for it to answer IAEA questions.
The IAEA says that, following its failed talks in Tehran last week, it has no plans for future talks with Iranian officials.
It said last Friday that "major differences" exist with Iran.
Western members of the IAEA fear that Iran has long been hiding a nuclear weapons programme behind its atomic energy activities, and that it is getting close to the scientific threshhold of being able to make an atomic bomb.
Tehran denies that it is pursuing nuclear weapons.
Israel, which is not part of the NPT and which has the Middle East's sole though undeclared nuclear arsenal, has threatened to attack Iranian atomic facilities.