The U.S. and its European allies share fears that Iran might be seeking the capacity to make atomic arms as it forges ahead with its nuclear program. But they differ on whether it is actively working on such weapons, reflecting the difficulties of penetrating Tehran's wall of secrecy.
Comments by U.S. intelligence officials indicate that Washington still thinks the Islamic Republic stopped such secret work nine years ago. But Britain, France and Germany disagree, even though their officials are keen to show that they and the United States speak with one voice on the concerns that Iran may want to produce nuclear arms.
Such divergence could mean trouble for the West's strategy to keep Iran nuclear weapons-free.
The United States _ and more forcefully Israel _ have warned that armed attack is possible if Iran is seen to be actively working on a bomb. But the lack of consensus among allies could complicate making any such assessment. That could slow a joint response _ or result in a misguided one.
Publicly at least, the United States is standing by a 2007 U.S. intelligence assessment that said Iran had abandoned attempts to develop a nuclear bomb in 2003.
A revised report last year remains classified. But in outlining its findings to Congress last year, National Intelligence Director James Clapper avoided any suggestion that the U.S. now thinks it erred in its 2007 assessment.
Instead he focused on Iran's expanding uranium enrichment and other programs monitored by the International Atomic Energy Agency as key concerns. Clapper said it's "technically feasible" that Tehran could produce a nuclear weapon in one or two years if its leaders decide to build one, "but practically not likely."
However, recent reports by the IAEA _ the U.N. nuclear agency _ explicitly challenge the U.S. view that any weapons development work was in the past. They say that some such activities "continued after 2003; and that some may still be ongoing."
The IAEA has not said what suspect work was conducted when. But in its most recent report last week, it repeated suspicions Iran may have:
_ worked on computer modeling of a core of a nuclear warhead
_ prepared for a nuclear weapons test
_ worked on development of a nuclear payload for a missile that could reach Israel.
_ conducted high-explosives testing at the Parchin military complex to set off a nuclear charge.
IAEA requests to visit the Parchin complex were denied by Iran twice this month, and diplomats accredited to the IAEA said Wednesday the agency is seeing unusual activity from satellite images of the site.
One of the diplomats, who demanded anonymity because his information was confidential, told the AP there were suspicions that Iran was trying to clear the area of any evidence of clandestine work, but added the IAEA had no evidence that movements reflected such attempts.
He quoted IAEA chief inspector Herman Nackaerts as telling a closed briefing that the suspected "ongoing activities" added "urgency" to his agency's attempts to visit.
In Tehran, the official IRNA news agency cited Iran's nuclear chief, Fereidoun Abbasi, as saying that no atomic activity had occurred at Parchin, southeast of Tehran. But he said that opening the site rested with the armed forces.
Israel is the most public in backing the view that weapons work is continuing in Iran as it seeks to energize international public resolve to counter Tehran's nuclear drive _ and possibly pave the ground for an armed strike.
Former Mossad chief Danny Yatom told The Associated Press that the Americans have privately acknowledged that their 2007 assessment was wrong, and said: "The Iranians have never stopped their efforts to achieve military nuclear capability."
Other U.S. allies are more circumspect _ but also back the IAEA view that secret weapons work may be continuing into the present.
A British official told The Associated Press that London and Washington had the same analysis on Iran. But the official, who asked for anonymity in exchange for commenting on the confidential report answered "yes" when asked if his country agreed with the IAEA assessment.
Public statements by some British officials go even further. In a blunt statement on Iran during a visit to Washington in January, Defense Secretary Philip Hammond said his "working assumption is that they are working flat out" to produce a nuclear weapon.
Diplomats accredited to the IAEA, who also asked they not be named because of the sensitivity of the issue, said France and Germany also believed some work continued past 2003, and possibly into the present.
Complicating the picture, there are signs the U.S. may be continuing to act as a main intelligence source for the IAEA's case that Iran's weapons work is continuing _ even while publicly standing by earlier conclusions that Iran stopped nine years ago.
A senior international official refused to say directly whether Washington is providing intelligence that backs up such suspicions. He did say, however, that the United States is one of the main sources on Iran's atomic weapons work, and that the agency keeps "getting information about such activities after 2003 from all ... sources." He asked for anonymity because his information is confidential.
Experts note that U.S. intelligence sees disagreement among Iran's leaders on whether to build a bomb or just work to reach that capacity. That, they say, might even mean that some groups may be working on weapons without the knowledge of others.
"I'm not even sure the Iranians know themselves," says Bruno Tetrais, a senior research fellow with the French-based Foundation for Strategic Research. "There may be different factions with different objectives."
There is more clarity about Iran's nuclear enrichment program.
Iran has enriched tons of fuel-grade material since its clandestine program was discovered 10 years ago. More recently, worries have been compounded by its decision two years ago to start enriching at a higher level that can be turned into fissile warhead material much more quickly and easily than its low enriched uranium.
Its total low and higher-level stockpile is now enough for four weapons _ and is growing daily.
In Washington last week U.S. Defense Secretary Leon Panetta, the former CIA director, said an Iranian decision to build a nuclear weapon "is the red line that would concern us and that would ensure that the international community, hopefully together, would respond," he said.
"We will not allow Iran to develop a nuclear weapon," he told the House Appropriations defense subcommittee.
But nuclear proliferation expert David Albright said that any breaching of the U.S. red line may only become obvious "when Iran makes a move to break out" by kicking out IAEA inspectors and
openly diverting its low-enriched uranium stockpile to produce weapons-grade uranium deep underground and safe from attack.
"The warning time may not be great between such steps and the time they actually have the bomb," he said.
For Yatom, the ex-Mossad head, the time to stop Iran through diplomacy may already have passed.
"They have the know-how, the technology, the infrastructure, everything," he says. Once they decide to build a bomb, they will be able to build a bomb _ unless somebody stops them."
Douglas Birch in Washington, David Stringer in London, Josef Federman in Jerusalem and Elaine Ganley in Paris contributed to this report.
George Jahn can be reached at http://twitter.com/georgejahn