Iran has denied misleading the UN nuclear watchdog over the extent of its experiments with plutonium.
Iran insists its nuclear programme is for peaceful purposes
The International Atomic Energy Agency accused Iran of experimenting with the nuclear material after a 1993 deadline.
Iran said that research on separating plutonium ended in 1993, and only "laboratory experiments" continued after that date.
The head of the IAEA stood by the agency's verdict, saying all Iranian nuclear work must be clearly reported.
"The fact remains that we need absolute correct dates and do not need stories to change," said Mohamed ElBaradei.
"Confidence is built when you feel you are getting full transparency and the story is not changing," he added.
IAEA official Pierre Goldschmidt reported earlier this week that Iran continued experiments on purifying one bottle of plutonium solution in 1995 and another in 1998.
'No need for plutonium'
On Friday Iran's chief nuclear negotiator, Hassan Rowhani, dismissed the dispute as "a technical matter... not even worth mentioning".
"We are talking about laboratory experiments, about microgrammes," he insisted.
"The IAEA wanted a secondary report, which is why we gave then a more detailed report on what was carried out after 1993.
"The Islamic Republic of Iran does not need plutonium, it was only for the laboratory and scientific work."
In an interview for the BBC's Newsnight programme earlier this week, Akbar Hashemi Rafsanjani, favourite to win a presidential election currently underway in Iran, said it was "possible" that Iran had not reported all experiments to the IAEA.
But he hit back at the body, accusing it of neglecting its duty to help Iran make peaceful use of nuclear technology.
Iran is seeking the closure of a two-year UN investigation into its nuclear programme, which it says is solely for peaceful civilian purposes.
The US has threatened to refer Iran to the UN Security Council for sanctions over what Washington says are plans to build a nuclear bomb.