A report from the International Atomic Energy Agency also indicated that nuclear inspectors have made little progress on clearing up other worrying aspects of Tehran's past nuclear activity.
Meanwhile, Iran's President Mahmoud Ahmadinejad said Thursday that his country is ready to discuss "mutual concerns" over its nuclear program and claimed the West had given in to the will of the Iranian nation.
"International monopolists (the U.S. and its allies) have been defeated in the face of your resistance and solidarity and have been forced to acknowledge your dignity and greatness," Ahmadinejad said in a speech before thousands of people in Qazvin, west of Tehran.
Specifically, the three-page report said Iran still had declined to answer requests to clarify statements by Ahmadinejad that his country had experimented with advanced centrifuges that speed up enrichment,
Iran also has refused to provide extra information on a document showing how to compress fissile material into the shape of warheads, said the confidential report circulated among the IAEA's 35 board member nations and made available to The Associated Press.
It declined also requests for key interviews with nuclear officials linked to potentially worrying finds by IAEA inspectors, and had not met additional requests for more information on an experimental enrichment project and tests and documents that could have nuclear weapons applications.
A senior U.N. official familiar with the report, who demanded anonymity in exchange for discussing its confidential contents, said it contained nothing that significantly hardens or diminishes concerns about its nuclear ambitions since the last IAEA report in late April.
The report, by IAEA chief Mohamed ElBaradei, was prepared for Monday's board meeting of the agency and amid delicate diplomatic maneuvering by six world powers focused on enticing Tehran into negotiations aimed at ultimately persuading it to give up enrichment domestically.
EU foreign policy chief Javier Solana on Tuesday gave Iranian officials a package of potential rewards if Tehran meant to persuade the Islamic republic to negotiate on enrichment and other nuclear issues.