As the International Atomic Energy Agency (IAEA) prepares to publish its latest report on its long-running investigation into Iran's disputed atomic drive, diplomats said they expected no real progress on the alleged studies, a key issue still to be resolved regarding Tehran's past nuclear activities.
Tehran has insisted that a series of recent visits by the IAEA inspectors to discuss the issue had gone well.
But one western diplomat, speaking on condition of anonymity, told AFP Tehran had moved little beyond asserting that the allegations were baseless and that the intelligence used to back them up was fake.
The United States' envoy to the IAEA, Gregory Schulte, told reporters this week that Washington would not be satisfied with that and wanted to see a detailed response to the allegations.
The United States also wanted to see readiness on Tehran's part to implement the so-called Additional Protocol, part of the Nuclear Non-Proliferation Treaty (NPT) which gives IAEA inspectors the right to carry out unannounced checks at nuclear sites.
"And we're also waiting to see whether Iran is prepared to suspend uranium enrichment," a process used to make the fissile material for an atomic bomb, Schulte said.
The IAEA's last report on Iran in February signed off most of the key questions over Tehran's past nuclear activities. But it demanded the Islamic republic present evidence to disprove reports that it had engaged in weaponisation studies.
The IAEA's deputy director general Olli Heinonen "made clear that continuing Iranian claims of 'baseless allegations' would not be acceptable," said Schulte.
"The board's expectations are equally clear: Iran's leaders must fully disclose their past activities and allow IAEA inspections to verify they are stopped."
The IAEA's latest report is set to be circulated to the board early next week so that it can be discussed at a full board meeting at the beginning of June.
The report will likely confirm again that Tehran has ignored UN Security Council demands to halt uranium enrichment, despite three rounds of sanctions.
Iran insists its nuclear program is aimed at generating power for civilian use.
Intelligence sources told AFP that Iran has begun experimenting with a new, more efficient type of uranium-enriching centrifuge at its main nuclear plant in Natanz.
Prototypes of the centrifuge, dubbed IR-3, have been seen by IAEA inspectors, said one diplomatic source close to the Vienna-based body.
Several of the machines "have already been installed," the intelligence source said.
"The Iranians are working at the site around the clock in order to obtain immediate results," the source said. "Checks as to the centrifuges' proper functioning have reached the final stage."
The IR-3 is larger and, Iran claims, more efficient than the preceding generation of centrifuge, the IR-2, which was Tehran's own modified version of western P2 centrifuges.
Iran had to design and build its own version of the P2 because a trade embargo made it difficult to get the foreign-made parts needed.
However, most of the 3,000 centrifuges confirmed as up and running in Natanz are of the original P1 type, which are much less reliable, and Tehran has only installed a small number of the IR-2s.
On April 8 Iran's President Mahmoud Ahmadinejad announced that Iran was working to install a further 6,000 centrifuges in Natanz, but observers say Tehran's progress in enrichment may be less advanced than officials claim.
