"This is ironic since the Iranians are the ones who want the file on them to be closed," a diplomat close to the Vienna-based International Atomic Energy Agency (IAEA) and who asked not to be named told AFP Tuesday.

During a visit by IAEA chief Mohamed ElBaradei to Tehran in April, Iranian Foreign Minister Kamal Kharazi had said Tehran expected the IAEA investigation to be completed in June ahead of a meeting of the IAEA board.

But an earlier delay to a crucial round on inspections in March "threw us out of sequence," an official close to the IAEA said, adding key results would not now be available for the board of governors meeting in Vienna June 14.

"It takes a long time time to get analysis of environmental samples (swipes to find traces of radioactive particles) so there is no way to get results in June in order to wrap this thing up," a Western diplomat said.

The Iranians have "succeeded in slowing down the (investigation) machine," a second Western diplomat said.

ElBaradei has said he hopes the IAEA can finish its investigation by the end of the year, but he warned in a CNN interview Saturday that Iran's cooperation so far had been insufficient.

"The jury is still out," he said about whether Iran's nuclear program is peaceful as Tehran has insisted.

Iran delayed inspections after the IAEA board in March condemned the country for failing to report key activities, particularly its acquiring of blueprints for sophisticated centrifuges to enrich uranium, which can be used in both civilian reactors and to make atomic bombs.

Iran had also failed in a report filed in October to fully disclose, as it had promised, its nuclear activities.

One diplomat said that while the international community may tolerate a lack of resolution on Iran's nuclear program until the US presidential elections in November, the issue "cannot go on forever. We are not going to debate on this for the next three years."

Diplomats were wary of speculating about whether Washington was backing off from pushing for the IAEA to take Iran to the UN Security Council for possible sanctions over its nuclear program due to the Iraq conflict.

Washington, which charges Iran is hiding attempts to make nuclear weapons, did not lobby for this at the last IAEA meeing in March and is not expected to insist on it in June.

Iran is close to the majority Shiite community in Iraq, which is crucial to securing peace there.

A diplomat said one thing sure was that "the Iranians are more confident because they know they're needed in Iraq."

IAEA inspectors now say they can see a pattern of radiation contamination in Iran which could indicate attempts to enrich uranium to bomb-grade level, diplomats said.

But the agency is waiting for another, more complete report from Iran on its nuclear program, which will take "half a year to a year" to evaluate, the official close to the IAEA said.

IAEA inspectors have so far reported two concentrations of particles of highly enriched uranium -- at a Kalaye Electric Company workshop in Tehran and at the Natanz pilot fuel enrichment plant 250 kilometres (150 miles) south of the capital.

Diplomats have confirmed other sites have been found, although details have not been made available.

WAR.WIRE