By Jim Muir
BBC correspondent in Tehran
Iran's top security official says Tehran is not obliged to tell the UN's nuclear watchdog of plans to build centrifuges for enriching nuclear fuel.
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Hassan Rohani, who also handles Iran's nuclear 'file', further denied polonium - a nuclear-blast trigger - was being used to enrich the fuel.
A report by the International Atomic Energy Association (IAEA) has accused Iran of hiding its nuclear intentions.
Iran's government agreed last year to fully disclose its nuclear plans.
The IAEA's report to its board of governors, who are due to meet in early March, complained that Iran had not declared to the agency that it had designs for advanced P-2 centrifuges.
Nor, according to the report, did it declare that it had produced polonium - a material that can be used to trigger nuclear explosions.
In reply, Mr Rohani said that the country was under no obligation to declare research on P-2 centrifuges, which it had not developed.
He also denied Iran had been using polonium for enrichment, saying that that too had only been at research stage.
He said Iran was pursuing other research projects which it had also not declared to the IAEA because it saw no need to do so.
As for accounting for the traces of highly-enriched uranium discovered by agency inspectors at several sites in Iran, Mr Rohani said that all the traces found - apart from some very low-enriched ones - had come on contaminated parts bought on the black market from abroad.
Therefore, he said, the IAEA should look elsewhere for answers.
He praised the level of co-operation between Iran and the Agency and said he expected the IAEA to move towards a final resolution of the Iran issue.
The Iranian Foreign Ministry spokesman meanwhile said that the points raised in the IAEA report were mainly matters of form which did not cast doubt on the peaceful nature of Iran's nuclear programme.
But on the polonium issue, he said that it was an unfinished research programme going back thirteen years and there had been a misunderstanding, he said, which would soon be removed.
The IAEA report urged Iran to intensify its co-operation in order to clarify outstanding questions.
But Iranian officials appear confident that, despite American pressures, they will avoid being referred by the IAEA to the United Nations for being in breach of their Non-Proliferation Treaty obligations.