Inspectors from the International Atomic Energy Agency will be completing their "assessment later this month," IAEA spokesman Mark Gwozdecky said Saturday, with little more than a week left in May.
At stake is what the IAEA's 35-nation board of governors will decide when it meets at the agency's headquarters in Vienna on June 14.
The United States claims Iran is hiding a program to build the bomb and has called for the IAEA, which has been investigating the Iranian program since February 2003, to refer the Islamic Republic to the UN Security Council for possible international sanctions.
Iranian ambassador Pirooz Hosseini told AFP Saturday that Iran had submitted late Friday a lengthy declaration on its nuclear program, in comments confirmed by the IAEA.
The report follows one by Iran last October that failed to live up to Iranian promises to fully disclose its nuclear activities, leaving out such sensitive information as Iran's possession of designs for sophisticated P-2 centrifuges that can enrich uranium to bomb-grade levels.
Iranian Foreign Minister Kamal Kharazi has said Tehran expects the IAEA probe to be completed by June.
But diplomats in Vienna said the new Iranian declaration had come too late for the IAEA to be able to evaluate it fully before the board meeting.
One diplomat said the evaluation would involve difficult technical analyses and follow-up tests that could take from half a year to a year.
And the UN atomic agency will be unable to make a final finding on Iran at the June meeting not only because of the late date of the Iranian declaration but also due to Tehran's delaying international inspections, diplomats said.
A delay to a crucial round of inspections in March "threw us out of sequence," an official close to the IAEA said, adding that inspections will have to continue past June.
Iran delayed inspections after the IAEA board in March condemned the country for failing to report key activities such as the P-2.
Gwozdecky said the Iranians had filed their declaration under an additional protocol to the nuclear Non-Proliferation Treaty (NPT) that mandates tougher inspections.
"This declaration should provide broader information about Iran's nuclear and nuclear-related activities and will facilitate the IAEA's assessment of the correctness and completeness of information already provided by Iran on its past and present nuclear activities," Gwozdecky said.
Iran claims it is solely seeking to develop nuclear energy for peaceful electricity production and needs to enrich uranium as fuel for reactors.
Hosseini said the Iranian declaration had provided information on "the capacity of uranium mines" in Iran, and, regarding nuclear installations, had given "a description of each building and places in sites that have been declared to the agency" as well as "information related to past activities."
IAEA inspectors see a pattern of radiation contamination in Iran which could indicate attempts to enrich uranium to bomb-grade level, diplomats close to the agency have told AFP.
IAEA inspectors have reported two such concentrations -- at a Kalaye Electric Company workshop in Tehran and at the Natanz pilot fuel enrichment plant 250 kilometres (150 miles) south of the Iranian capital.
Diplomats have confirmed to AFP that other sites have been found.
But they have not provided details, and one diplomat downplayed the possibility that the IAEA has found a "smoking gun" to prove Iran is secretly developing nuclear weapons.
Iran claims the contamination from particles of enriched uranium is from equipment it imported through an international black market.