Although international concern is growing about Iran's nuclear program and its regional ambitions, diplomats here say most U.S. intelligence shared with the U.N. nuclear watchdog agency has proved inaccurate and none has led to significant discoveries inside Iran.
The officials said the CIA and other Western spy services had provided sensitive information to the Vienna-based International Atomic Energy Agency at least since 2002, when Iran's long-secret nuclear program was exposed. But none of the tips about supposed secret weapons sites provided clear evidence that the Islamic Republic was developing illicit weapons.
"Since 2002, pretty much all the intelligence that's come to us has proved to be wrong," a senior diplomat at the IAEA said. Another official here described the agency's intelligence stream as "very cold now" because "so little panned out."
The reliability of U.S. information and assessments on Iran is increasingly at issue as the Bush administration confronts the emerging regional power on several fronts: its expanding nuclear effort, its alleged support for insurgents in Iraq and its backing of Middle East militant groups.
The CIA still faces harsh criticism for its prewar intelligence errors on Iraq. No one here argues that U.S. intelligence officials have fallen this time for crudely forged documents or pushed shoddy analysis. IAEA officials, who openly challenged U.S. assessments that Saddam Hussein was developing a nuclear bomb, say the Americans are much more cautious in assessing Iran.
American officials privately acknowledge that much of their evidence on Iran's nuclear plans and programs remains ambiguous, fragmented and difficult to prove.
The IAEA has its own concerns about Iran's nuclear program, although agency officials say they have found no proof that nuclear material has been diverted to a weapons program.
Iran's Islamist government began enriching uranium in small amounts in August in a program it says will provide fuel only for civilian power stations, not nuclear weapons.
On Thursday, the IAEA released a report declaring that Iran had expanded uranium enrichment and defied a Security Council deadline to suspend nuclear activities. In the meantime, the agency is locked in a dispute with Tehran over additional information and access to determine whether the program is peaceful.
In November 2005, U.N. inspectors leafing through papers in Tehran discovered a 15-page document that showed how to form highly enriched uranium into the configuration needed for the core of a nuclear bomb. Iran said the paper came from Pakistan, but has rebuffed IAEA requests to let inspectors take or copy it for further analysis.
Diplomats here were less convinced by documents recovered by U.S. intelligence from a laptop computer apparently stolen from Iran. American analysts first briefed senior IAEA officials on the contents of the hard drive at the U.S. mission here in mid-2005.
The documents included detailed designs to upgrade ballistic missiles to carry nuclear warheads, drawings for subterranean testing of high explosives, and two pages describing research on uranium tetrafluoride, known as "green salt," which is used during uranium enrichment. IAEA officials remain suspicious of the information in part because most of the papers are in English rather than Persian, the Iranian language.
"We don't know. Are they genuine, are they real?" asked a senior U.N. official here. Another official who was briefed on the documents said he was "very unconvinced."
Iran's representative to the IAEA, Ali Asghar Soltanieh, dismissed the laptop documents as "fabricated information." Iran, he said, has produced 170 tons of "green salt" at a uranium conversion facility in Esfahan that is monitored by the IAEA.
"We are not hiding it," he said in an interview. "We make tons of it. These documents are all nonsense."
The U.S. government is not required to share intelligence with the IAEA, and relations between Washington and the U.N. agency are at times testy. In March 2003, IAEA chief Mohamed ElBaradei embarrassed the White House when he told the U.N. Security Council that documents indicating Hussein's government in Iraq had sought to purchase uranium in Niger were forged. The Bush administration subsequently opposed ElBaradei's reappointment to his post.
While it confronts Iran's nuclear ambitions, the Bush administration also has tried to implicate Iran as a supplier of munitions and training for insurgent groups in neighboring Iraq.
But the quality of its information has limited this effort too.
U.S. officials recently compiled evidence purporting to show that the Iranian Quds Force, an elite unit of the Revolutionary Guard, had supplied Iranian-made weapons to Shiite militias that have attacked U.S. forces in Iraq.
After U.S. officials unveiled the evidence to reporters in Baghdad two weeks ago, however, Secretary of Defense Robert M. Gates and other Pentagon officials scrambled to retreat from the incendiary claim that the "highest levels" of the Tehran government were directly involved.
"I don't know if it goes to the highest levels of the government," Army Lt. Gen. Raymond T. Odierno, the officer in charge of daily operations in Iraq, told Pentagon reporters Thursday. "What we do know is that the Quds Force has had involvement with some extremist groups in Iraq."
Washington has sought to pressure Tehran into halting the supply of "explosively formed projectiles" that are able to penetrate heavily armored vehicles. The projectiles represent only a small percentage of roadside bomb attacks in Iraq, but they are far more lethal than ordinary explosives.
Administration officials also cite a growing effort by the militant group Hezbollah, an Iranian protege and ally based in Lebanon, to aid anti-American Shiite forces in Iraq.
U.S. military officials contend that Hezbollah has provided training in Lebanon to hundreds of members of the Al Mahdi militia, which is controlled by radical anti-American cleric Muqtada Sadr. A smaller number of Hezbollah forces reportedly have entered Iraq through Syria to provide such training.
The administration has ordered a second aircraft carrier group into the Persian Gulf, a reminder that President Bush could order an airstrike on Iran's nuclear sites even while U.S. forces are tied down in Iraq. But White House officials have denied that an attack is imminent.
Given the lack of clear evidence, Iran's strategic goals in Iraq are a matter of debate, and concern has spread about its growing influence there. Although Iran is mostly Persian and Iraq is mostly Arab, both have majority Shiite populations that have kept close religious, economic and cultural ties for centuries. Iran's rulers view the U.S. as meddling in their backyard, or at least in their sphere of influence.
Some outside experts think the Islamic Republic seeks to keep the United States tied down indefinitely in Iraq and will actively resist a settlement there for fear that Washington will next turn its guns on Iran.
Ali Ansari, an expert on Iran at St. Andrews University in Scotland and author of "Confronting Iran," counters that Iran and America share some interests.
Iran is "looking for a stable Iraq," he said. "They want an Iraq that is not fragmented. But the difference would be that they don't want an Iraq that is militarily strong. They want an Iraqi government that is elected democratically, which means a Shia Iraq."
But Sunni-dominated governments in Egypt, Jordan and especially Saudi Arabia have pushed the U.S. to expand Sunni representation in Iraq's leadership as a way of countering Tehran. Some experts fear that a nuclear-armed Iran would spark a regional arms race.
John D. Negroponte, former director of national intelligence, told a House committee last month that Iran had extended its "shadow in the region" since the U.S. ousted hostile regimes on its borders: the Taliban in Afghanistan and Hussein's government in Baghdad.
Iran also has increased regional political leverage, he said, because of increased oil revenues, electoral victories by Hamas in the Palestinian territories and Hezbollah's "perceived recent success in fighting Israel" in Lebanon.
Iran and Syria since have resupplied arms to Hezbollah, including stocks of long-range missiles that could reach deep into Israel, U.S. officials contend.
Washington lists both Hamas and Hezbollah as terrorist organizations.
The administration has also become alarmed by Iran's increasing efforts to support Hamas after the group's victory in Palestinian elections in January 2006. That worry lies behind an $86-million U.S. plan to build up Palestinian Authority President Mahmoud Abbas' Presidential Guard and national security forces, rivals to Hamas.
Iran's president, Mahmoud Ahmadinejad, has successfully exploited the growing confrontation with Washington to gain much needed political support at home. Nationalist sentiments run deep in Iran and the claim that Tehran has the same right to nuclear power as other nations has become a rallying cry that undermines the government's domestic critics.
"None of us can accept the suspension of these activities because people consider this our legal right," said Akbar Alami, an independent lawmaker. "All the political parties agree with this. We cannot stop."
Ahmadinejad's fiery rhetoric and defiance of the West also have burnished his credentials as a populist leader in other Islamic nations. That has raised alarms in Sunni governments around the region that Iran's brand of militant political Islam, potentially backed by the prestige of being a nuclear power, is on the march.
"The Americans are worried about enriched uranium, and the Arabs are worried about enriched Shiism," said Mamoun Fandy, senior fellow for Persian Gulf security at the London-based International Institute for Strategic Studies. Iran's growing power, he said, "threatens every existing political order in the region."
Drogin reported from Vienna and Murphy from London. Times staff writers Paul Richter and Peter Spiegel in Washington contributed to this report.