VIENNA, Austria -- Iran has assembled hundreds of advanced machines reflecting a possible intention to speed up uranium enrichment, diplomats have said.
One diplomat said more than 300 of the centrifuges have been linked up in two separate units in Iran's underground enrichment plant and a third was being assembled. He said the machines apparently are more advanced than the thousands already running underground, suggesting they could be the sophisticated IR-2 centrifuge that Tehran recently acknowledged testing.
But a senior diplomat said that while the new work appeared to include advanced centrifuges, they were not IR-2s. He added that it was unclear whether the machines were above or below ground.
The location is significant, because the aboveground site at Natanz is for experimental work and the underground facility is the working enrichment plant.
A third diplomat -- who like the other two closely follows Iran's nuclear program -- confirmed that Iran had started linking up advanced centrifuges in a configuration used for enrichment. But he said all remained above ground and none of the machines were running.
Uranium enrichment can produce both fuel for power plants and the fissile core of nuclear warheads. Tehran insists its nuclear program is intended only to produce energy, but there is growing international concern that it could lead to the development of weapons.
Two of the diplomats spoke to the AP earlier this week and the third Thursday. All are linked to the Vienna-based International Agency for Atomic Energy, the U.N. nuclear watchdog, but asked for anonymity because their information was confidential.
Their reports underlined Iran's determination to push ahead with its enrichment program despite U.N. Security Council sanctions. One of the diplomats said officials in Tehran would likely detail the new centrifuge work on April 8, which Iran has designated National Nuclear Technology Day.
Preliminary assembly is only a first step in the complex enrichment process; in comments to the AP earlier this year, Ali Ashgar Soltanieh, Iran's chief delegate to the IAEA, acknowledged that his country's uranium enrichment program was experiencing "ups and downs." It appeared to be the first time Iran admitted its enrichment activities were facing difficulties.
It was unclear whether the linkups of the more advanced centrifuges would ever be used to churn out enriched uranium or whether they were only experimental configurations.
"Something new is definitely going on," said former U.N. nuclear inspector David Albright, whose Washington-based Institute for Science and International Security tracks countries under nuclear suspicion.
Albright said that with information contradictory on the type of centrifuge, it was difficult to speculate on the significance of the new work.
In comments to the AP earlier this week, the first diplomat said two linkups or "cascades" of 176 centrifuges each had recently been assembled and a third was in the process of being put together.
The workhorse of Iran's enrichment program is the P-1 centrifuge which is run in cascades of 164 machines. But Iranian officials confirmed in February that they had started using the IR-2 centrifuge that can churn out enriched uranium at more than double the rate.
The February announcement was the first official confirmation by Tehran after officials at the IAEA reported that Iran was using 10 of the new IR-2 centrifuges to produce small amounts of enriched material.
Ten centrifuges are too few to produce enriched uranium in the quantities needed for an industrial-scale energy or weapons program and far below the 3,000 older P-1 centrifuges in Iran's underground enrichment plant in the central town of Natanz.
Although a U.S. intelligence summary late last year concluded that Tehran stopped working on direct nuclear weapons programs in 2003, enrichment is of concern because it can produce weapons grade uranium for the core of warheads.
The IAEA highlighted the "new-generation centrifuges" in its February report on Iran but did not provide details on their operation.