Non-proliferation expert Mark Fitzpatrick said: "In various ways, Iran is pushing the envelope toward the very edge of what are absolute legal requirements."
Fitzpatrick, an analyst at the International Institute of Strategic Studies think tank in London, said that Iran would now not have to report future modifications at Natanz, where it aims to ultimately have over 50,000 centrifuges running.
By Michael Adler
VIENNA -- Iran's threat to limit cooperation with the UN nuclear watchdog comes as international inspectors seek greater access to a key underground site for enriching uranium.
Diplomats said that Iran's decision to stop giving immediate notification of its nuclear plant building plans means that Tehran could now work on new strategic sites without informing the International Atomic Energy Agency (IAEA), which could help Iranian authorities to hide facilities from possible military airstrikes.
The United States, which charges that Iran's nuclear energy program is a cover for secretly developing nuclear weapons, has not ruled out military action.
The UN Security Council imposed new sanctions against Iran Saturday over its refusal to suspend uranium enrichment. Iran responded Sunday by saying that it would limit cooperation with the IAEA.
A Tehran government spokesman said that it would no longer inform the nuclear watchdog of new installations until six months before they are brought into service.
It was not immediately clear how this would affect attempts to monitor work on a plant at Natanz in central Iran. Iran is building in Natanz an industrial-scale plant to make enriched uranium, which can be used for nuclear fuel or as atom bomb material.
Iran has notified the IAEA of its plans to put in 3,000 centrifuges at the site, referring to the machines which arranged in production line cascades, enrich uranium.
IAEA inspectors were turned away from Natanz January 17, then visited January 20 but were not allowed to verify the number of centrifuge machines in operation and were visiting the site again Monday, diplomats said.
The IAEA has said that it needs to install cameras at Natanz to monitor the operation of centrifuges.
A 3,000-centrifuge facility could produce enough enriched uranium for one atomic bomb in less than a year.
A diplomat who closely monitors the IAEA verification effort said that January 20 "the inspectors were not allowed to have free access to the cascade area. They couldn't go and see the exact numbers."
Another diplomat said that the Iranians have "been awkward about letting inspectors go down the cascade lines in the past."
But a third diplomat stressed that the IAEA inspections were about verifying that there is no unreported feeding or withdrawal of nuclear material, and not to count centrifuges.
The first diplomat said that Iran has installed underground in Natanz six cascades of 164 centrifuges and was test-running four of the cascades without the uranium feedstock gas used to make enriched uranium.
This would mean that Iran has almost 1,000 centrifuges installed and is actively running well over 500.
Non-proliferation expert Mark Fitzpatrick said: "In various ways, Iran is pushing the envelope toward the very edge of what are absolute legal requirements."
Fitzpatrick, an analyst at the International Institute of Strategic Studies think tank in London, said that Iran would now not have to report future modifications at Natanz, where it aims to ultimately have over 50,000 centrifuges running.
IAEA officials refused to comment on Iran's latest withdrawal of cooperation until they had received official notification from Tehran.
But the first diplomat said that Iran's actions were "scary. They could go on working on secret sites without reporting."
Fitzpatrick said that the change in Iran's stance "comes at a time when they are likely building redundant facilities in the event an air attack destroys Natanz."
