The UN atomic energy agency has admitted wrongly reporting that Iran withheld information from it.
Mohamed ElBaradei called for more transparency from Iran
Iran has recently come in for strong criticism from the International Atomic Energy Agency (IAEA) and the United States over its nuclear programmes.
The IAEA reported in June that Tehran had failed to inform it about importing magnets for advanced centrifuges which can produce weapons-grade uranium.
However, it now says Iran made an oral statement about the magnets in January.
On Wednesday, the US has accused Iran of bullying foreign diplomats.
The US ambassador to the United Nations in Vienna, Kenneth Brill, said Iran's president was using "intimidation" by saying Tehran might resume its uranium enrichment programme.
Admitting the mistake on Thursday, IAEA deputy director general Pierre Goldschmidt said the agency "acknowledges that it omitted to take notice of the oral statement made in January with respect to the importation of magnets".
But IAEA Director General Mohamed ElBaradei played down the importance of the admission.
"This is not a major mistake. Iran could have corrected it," he said.
He added that "this technical correction doesn't change the fact that we need more transparency from Iran" in reporting on its nuclear programme.
The IAEA is investigating US charges that Iran is secretly developing nuclear weapons.
Hossein Mousavian, secretary of the foreign policy committee of Iran's Supreme National
Security Council, said: "This has been a big mistake."
He was speaking on the sidelines of an IAEA meeting that is expected to issue a resolution that criticises Tehran for its patchy co-operation.
Mr Mousavian welcomed the correction but said it came too late and the inaccurate report had tainted the whole atmosphere of the meeting.