The Vienna-based International Atomic Energy Agency ordered Iran to prove by Friday that its nuclear activities are not aimed at building a weapons arsenal, as the United States contends.
In response, Tehran last week handed over a dossier with information about the program. But the agency can't yet judge whether the country has complied with its demands because it has not yet been able to fully verify the report, spokeswoman Melissa Fleming told The Associated Press.
"There's not going to be any action" on Friday when the deadline expires, she said.
A complete analysis could take weeks, Fleming said, adding it was "difficult" to say when it would be finished. The process will "not necessarily" be completed by Nov. 20, when the IAEA's board meets to assess the situation, she said.
As a signatory of the Nuclear Non-proliferation Treaty, Iran is prohibited from developing nuclear weapons.
"The Iranians have stated that they have already turned over a full and complete declaration of their past nuclear activities," Fleming said. "The IAEA is intensively working to scrutinize that declaration and verify the claims made. There was no expectation that that work would be done by Friday."
IAEA Director-General Mohamed ElBaradei said in an interview for Friday's editions of the German newspaper Frankfurter Allgemeine Zeitung that he hoped Iran's claim that the report is complete would turn out to be true.
"But we're still examining the report," he was quoted as saying. "We're not yet in a position to give a clear judgment."
ElBaradei told the newspaper his agency would be able to answer some questions at the Nov. 20 meeting, but that it "would have to investigate other issues after November."
Fleming told The AP that the most difficult part of the analysis was the investigation of the origins of traces of highly enriched weapons-grade uranium found in Iran by agency experts.
Iran insists the traces, found in environmental samples, were inadvertently imported on equipment meant to generate electricity.
"There are a number of very complicated technical issues that require complicated technical processes to fill in the blanks and connect the dots," she said. "We will not be in a position to evaluate the fullness and completeness of that declaration until we have had the chance to fully verify it."
A report to be issued ahead of the agency board's meeting would contain more details, but it "might not necessarily provide the final information," Fleming said.
"The report will certainly offer a great deal of detail and fill in some key blanks," she said. "We have done a tremendous amount of groundwork of our own."
Fleming declined to say whether the information in hand would be enough for board members to make a decision on whether to report Iran to the U.N. Security Council, which has the power to impose sanctions.
"It's going to be up to the member states to make a judgment on what they see in the report and how they want to handle the revelations that appear there," she said.
By Susanna Loof