The United States expressed concern on Friday on a new International Atomic Energy Agency report that said Iran recently understated how much uranium it had enriched.
The United States suspects Iran of trying to use its nuclear program to build an atomic bomb, but Tehran insists that is purely for the peaceful generation of electricity. Enriched uranium can be used to make a nuclear bomb.
"The report represents another lost opportunity for Iran as it continues to renege on its international obligations. Absent compliance, the international community cannot have confidence that this program is exclusively of a peaceful nature," White House spokesman Robert Gibbs told a news conference.
"The White House understands that -- working with our allies --
that this is an urgent problem that has to be addressed and we can't
delay addressing," Gibbs told reporters.
The IAEA reported Thursday that Iran has slowed down uranium enrichment activities, but has built up a stockpile of nuclear fuel.
A senior official close to the IAEA said that Iran's expansion of its enrichment plant in Natanz “has slowed down considerably.” The official said Iran did not provide any reason or explanation for that.
According the new IAEA's report on Iran’s nuclear activities, there are 3,964 centrifuges actively enriching uranium in the Natanz nuclear power plant, just 164 more than in November.
“We see the pace of installing and bringing centrifuges into operation has slowed quite considerably since August," a senior U.N. official said.
But Iran's reported stockpile of low-enriched uranium had risen to more than 1,000 kg from 630 kg in November and 480 kg in August. The heightened output rate suggested existing centrifuges were operating at higher capacity and more glitch-free than before.
Analysts calculate that anywhere between 1,000-1,700 kg would be needed to convert into high-enriched uranium suitable for one bomb.
The U.S. urged Iran to give up its enrichment activities and said Tehran's refusal to respond constructively to IAEA requests over its program was "deeply troubling."
"We view this report as another opportunity lost to resolve international concerns," U.S. State Department spokesman Gordon Duguid told reporters in Washington.
But Iran's ambassador to Vienna Ali Asghar Soltanieh told state news agency IRNA that the "latest report had nothing new.”
“Iran will fully cooperate with the IAEA but within the Non-proliferation Treaty (NPT) and its legal commitments,” Soltanieh said.
"The IAEA and its chief ... are expected to declare the inspections as normal and put an end to repetitive talks at the board of governors," he added.
But it would take Iran another two to five years before it is capable of producing nuclear weapons, IAEA director Mohamed al-Baradei said this week.
Al-Baradei suggested that Tehran's Iran had not added as many centrifuges recently as it could have and the reason was probably political rather than technical.
He was alluding to perceptions Iran may want to give Obama political cover for talks, not provoke harsher U.N. sanctions over its refusal to suspend enrichment.
No substantive progress
The IAEA nevertheless conceded that, despite six years of intensive investigation, it is no closer to determining whether Iran's disputed nuclear drive is entirely peaceful as Tehran claims.
"Regrettably, as a result of the continued lack of cooperation by Iran in connection with the remaining issues which give rise to concerns about the possible military dimensions of Iran's nuclear program, the agency has not been able to make substantive progress on these issues," the report said.
The main sticking point remain are the so-called "alleged studies"—documents collected from a wide range of intelligence sources that appear to suggest Iran may have been trying to develop a nuclear warhead, convert uranium and test high explosives and a missile re-entry vehicle.
The IAEA also reported that Iran was barring inspectors from doing checks at its planned Arak heavy water reactor.
Iran had built a dome at Arak which made it impossible to use satellite imagery to monitor building.
Western powers fear Iran may use the Arak reactor to derive plutonium from spent fuel rods as another source of atom bomb fuel. Tehran says the complex will be designed to produce isotopes for medicine and agriculture.
Iran has repeatedly dismissed the allegations as "baseless" and the evidence used to back them up as "fabricated."
The investigation has been stymied for over a year, said an unnamed senior official close to the IAEA. "It’s deep stalemate," the official said.