IAEA chief Muhammad al-Baradai previously indicated there were no signs that Parchin was a nuclear weapons site, but US officials said al-Baradai was not qualified to make such a statement without having inspected the site.
Last month, a prominent nuclear expert said analysis of recent satellite images showed that Parchin, 30km southeast of Tehran, could be a site for research, testing and production of nuclear weapons and should be closely inspected.
Iran dismissed the charge, insisting there were no nuclear activities at Parchin. It also denied ignoring UN requests to visit the site, saying inspectors had never asked to go there.
"They asked to go there and Iranians have told the IAEA that they can go to Parchin," a Western diplomat close to the IAEA told Reuters.
Inspections this month
It was unclear if the agency would be permitted to take
environmental samples to test for traces of nuclear materials,
but IAEA inspectors routinely take samples at all important sites to verify that no undeclared atomic work has been carried out.
A nuclear expert told Reuters - on condition of anonymity - inspectors were planning to go to Parchin this month, in time to include their observations of the site in next month's crucial progress report.
An IAEA spokeswoman declined to comment, saying that inspection locations and times were strictly confidential.
The IAEA could report Iran to the
UN Security Council next month
When the IAEA board of governors meets in November, it is expected to decide whether Iranian activities warrant a report to the UN Security Council.
Theoretically, the Security Council could then impose economic sanctions to pressure Iran.
An IAEA resolution passed last month demanded that Iran should answer all outstanding questions and provide prompt access to all sites agency inspectors wanted to visit.
While Iran is providing access, it has balked at the IAEA's
demand that it should freeze all activities on uranium enrichment.
Defiance in Tehran
On Friday, a leading Iranian cleric said his country would
never be bullied into giving up its nuclear programme, but denied having ambitions for weapons-grade development.
"Iran will never yield to international pressure to abandon
its home-grown nuclear technology," Ayat Allah Ahmad Jannati, who heads Iran's hard-line Guardian Council - a powerful, unelected supervisory body - told worshippers at prayers in Tehran.
"Americans should know that it is just impossible. You will take this wish to the grave," he added. "We have no intention of pursuing nuclear weapons."
Jannati said Iran would never
give up its nuclear programme
Washington says Tehran is developing weapons under cover of a civilian atomic energy programme and wants it reported to the Security Council. Tehran vehemently denies the accusation.
Iranian officials were not available for comment, but a
diplomat close to the negotiations said Iran had agreed in
principle to allow IAEA inspectors to visit all sites.