VIENNA, April 28 — Iran has drastically curtailed cooperation with nuclear inspectors over the past month as it has sped forward with its nuclear enrichment, the International Atomic Energy Agency said Friday.
Iran's failure to comply with a United Nations Security Council deadline to freeze all nuclear fuel enrichment by Friday all but guarantees a lengthy struggle in the Council over how to contain the country's nuclear ambitions.
Striking an unusually bleak tone in an eight-page report requested by the Council, the United Nations nuclear agency also documented its increasing difficulty in monitoring Iran's activities, and Iran's refusal to answer questions about suspected links between its civilian program and its military one.
For the first time, the agency stated that Iran had begun enriching uranium on a small scale, confirming Tehran's boasts.
Iran immediately vowed to resist all outside pressure. It repeated its demands that the world acknowledge that it has the legal right to enrich uranium under the terms of the Nuclear Nonproliferation Treaty, and start any negotiations from there.
"The facts on the ground have changed," Gholamreza Aghazadeh, chairman of the Iran Atomic Energy Organization, said in Vienna. He said uranium enrichment was "irreversible," rejecting again the Council's demand that Iran stop enriching uranium at its pilot plant at Natanz.
In Washington, President Bush said, "The Iranian government's intransigence is not acceptable." But he also added that "diplomacy is just beginning," an effort to allay concerns among his allies that he may be using the debate at the Council as a prelude to ordering a military attack on Iran's facilities.
Other American officials described a step-by-step approach, saying they planned to ask the Council as soon as next week to require Iran to stop nuclear enrichment under Chapter 7 of the United Nations Charter, which makes resolutions mandatory under international law and opens the way to sanctions or even military action. (The Friday deadline was part of a nonbinding resolution.)
Indeed, Britain immediately pledged to introduce a resolution next week for a mandatory order to Iran to stop enriching uranium.
Such a proposal is bound to accelerate the debate, with Russia and China balking at the use of Chapter 7. "We all know what Chapter 7 involves," said Wang Guangya, China's ambassador to the United Nations. "All we want is a diplomatic solution, so therefore I believe that by involving Chapter 7, it will be more complicated."
United States officials said Friday that the Iranians had miscalculated by defying the inspectors and added that they would seek sanctions even without Council approval.
"What they have done is created a coalition against them," R. Nicholas Burns, the under secretary of state who has led the diplomatic negotiations for the administration, said Friday. "They have forced a dynamic where there will have to be some action against them, whether it is in the Security Council or outside the Security Council, by like-minded nations."
He said the effort would focus on denying Iran conventional military equipment and "dual use" technology, which can be used for both nuclear and non-nuclear activity, and on cutting off international lending to Iran.
Mr. Bush referred to a nuclear weapons program in Iran as if it were a given. But Russia and China have argued that in the absence of hard evidence that Iran is pursuing a weapons program — evidence the atomic agency said it had been barred from searching for — this is not a matter of war and peace for the Security Council.
Although Iran, OPEC's second-largest oil producer, has said it does not intend to curb exports as a political weapon, crude oil prices rose above $72 a barrel on Friday after the release of the agency's report, before settling around $71.88.
Iran's leaders seemed emboldened rather than frightened by the latest threats of punitive measures.
"Those who want to prevent Iranians from obtaining their right should know that we do not give a damn about such resolutions," President Mahmoud Ahmadinejad told a crowd in Khorramdarreh on Friday.
The Iranians have expressed confidence that the international community is too divided to impose any meaningful punishment, and even if it did, Iran would be ready to suffer the consequences.
The nuclear agency has succeeded in pushing Iran gradually over time to disclose bits and pieces of its nuclear program. But this time around Iran has taken only minimal steps — and to the West, insufficient ones — to cooperate with the agency.
"After more than three years of agency efforts to seek clarity about all aspects of Iran's nuclear program, the existing gaps in knowledge continue to be a matter of concern," the agency's report said. "Any progress in that regard requires full transparency and active cooperation by Iran."
The report listed case after case where Iran had done nothing during a 30-day grace period to provide information that might clarify whether its nuclear activity is for civilian purposes, as it claims.
The agency, for example, has repeatedly asked Iran over the last three years to answer questions and provide documents and access on a wide range of issues as a way to build confidence that it did not have a hidden weapons program.
Since February, when the 35-nation board of the United Nations agency decided to report the case to the Security Council, Iran has severely curtailed its cooperation, halting voluntary visits to certain nuclear-related sites not covered under Iran's treaty obligations.
For example, "Gaps remain in the agency's knowledge" about the scope of Iran's centrifuge program, the report said. "With the information we have, we cannot proceed any further," one senior official told reporters about the centrifuge dossiers. "We are stuck."
The official ticked off a list of other areas where Iran had rebuffed the agency's requests for information, saying, "We haven't had any discussions in those areas in the last month." He added that such a tactic of minimal cooperation made it extremely difficult for the agency to verify whether Iran has secret, undeclared nuclear programs.
Indeed, the report referred to other information gaps that left the agency "unable to make progress in its efforts to provide assurance about the absence of undeclared nuclear material and activities in Iran."
The agency has also failed to get an explanation of a surprising boast by President Ahmadinejad this month that Iran was conducting research on the P-2 centrifuge method of making atomic fuel, a technology that Iran had previously declared it had abandoned.
Instead of providing information and access on the array of issues, in a letter to the agency delivered Thursday afternoon Iran said it would give the agency a timetable for cooperation in three weeks — but only if "the Iran nuclear dossier will remain, in full, in the framework of the I.A.E.A. and under its safeguards."
The letter is interpreted by some agency officials as a veiled threat that Iran could withdraw completely from the Nuclear Nonproliferation Treaty, and evidence that Iran is stalling for time, either to test the will of other nations or to try to restart negotiations — but only on its own terms.
Mr. Aghazadeh, who is also a vice president and a former oil minister, emphasized the need for more time to talk, saying, "We are willing to negotiate about the worries of the world and about removing the ambiguities about the nature and scope of our nuclear program."
The agency's report confirmed that Iran had completed a system of 164 centrifuges to enrich uranium at its plant at Natanz in March, adding that another two systems, or cascades, of the same size were under construction there.
The report said the agency had taken samples earlier this month at Natanz that "tend to confirm" the enrichment level of 3.6 percent declared by Iran — the level needed to make electricity.
Uranium must be about 90 percent pure for use in bomb-making, and thousands of centrifuges are needed to make enough for a weapons program. Nevertheless, the development is worrisome to nuclear experts.
Despite reports that Iran has had problems in getting its centrifuges to work, the senior official who discussed the report said: "What is relevant is that they got the first 164-centrifuge cascade up and running, and managed to produce low-enriched uranium. The 164 centrifuges continue to spin, as far as we know."
The report also said Iran may have received plutonium, which can be used to produce electricity or to make weapons, from a secret source.