The diplomats said the crews at Parchin may be trying to erase evidence of a test of a small nuclear-weapon trigger. They spoke on condition of anonymity because they were not authorized to discuss the information on the record.
The assertions added to tensions surrounding Iran's controversial nuclear program, which the West fears is geared toward nuclear weapons-making but Tehran insists is for peaceful purposes.
Mehmanparast dismissed the diplomats' assertions.
"Those who are familiar with nuclear physics know that these comments are not remarkable in any way," he said. "This is mainly public speculation and not based on logic."
"Basically, nuclear military activities are not cleanable, at all," Mehmanparast said. He did not directly address the satellite photos but stressed that Parchin has been continuing its "conventional military" activities and operations.
Inspecting Parchin, southeast of the capital Tehran, was a key request made by senior IAEA teams that visited Tehran in January and February. Iran rebuffed those demands at the time, as well as attempts by the nuclear agency's team to question Iranian officials and secure other information linked to the allegations of secret weapons work.
Iran said last week that a visit was possible once an unspecified set of conditions was reached. But an IAEA official said the agency had received no new offer from Iran on allowing such an inspection as of Tuesday. The official spoke on condition of anonymity because he was not authorized to comment publicly on confidential IAEA matters.
The Parchin complex has been often mentioned in the West as a suspected base for secret nuclear experiments - a claim Iran consistently denies. IAEA inspectors visited the site in 2005, but only one of four areas on the grounds and reported no unusual activities.
An IAEA report last year said there were indications that Tehran had conducted high-explosives testing to set off a nuclear charge at Parchin. Iran denied the atomic activity and insisted that any decision to open the site rests with the armed forces since it was a military, not nuclear, facility.
