Iran is facing concerted demands by the international community to be more transparent over its nuclear ambitions.
The IAEA wants Iran to be more open to inspections
European countries and the UN joined the US in criticising Iran for allegedly not keeping a pledge to suspend uranium enrichment activities.
UN atomic energy agency chief Mohamed ElBaradei said the "ball is very much in Iran's court to come clean".
The US accuses Iran of cynically pursuing nuclear weapons, but Tehran insists its programme is peaceful.
The enrichment process can be used for nuclear power plants or nuclear weapons.
The demands come a day after the UN's International Atomic Energy Agency (IAEA) presented a report on Iran's nuclear record to a meeting of member countries.
The agency highlighted Iran's refusal to allow nuclear inspectors to revisit a key military complex, at Parchin.
But Iran's chief delegate, Sirous Nasseri, responded saying concerns about information gathered at such inspections being leaked were "more intense in view of potential threats of military strikes".
Mr Nasseri was referring to speculation that Washington may be planning attacks on Iranian nuclear sites.
Iran was not obliged to allow inspectors access to sites such as Parchin, he noted.
Mr ElBaradei said it was now up to Tehran to dispel doubts about its programme "through absolute transparency measures and co-operation with the [IAEA]".
"If I say there are three more important things Iran needs to do, I should say transparency, transparency and more transparency," he said.
France, the UK and Germany, the three European countries who are leading negotiations with Tehran on the issue, expressed concern about Iran's recent cleaning and quality control work on centrifuge parts.
Robert Wright, heading the UK delegation to the IAEA meeting, urged Iran to keep its pledge to suspend activities linked to uranium enrichment.
"We understand this decision as a voluntary commitment to suspend all, meaning each and every, enrichment-related activities. We urge Iran to keep to this voluntary commitment," he said.
The US ambassador at the IAEA, Jackie Sanders, said Tuesday's report provided a "startling list" of Iranian attempts to hide and mislead.
"The IAEA is still not able to provide assurances that Iran is not pursuing clandestine activities at undeclared locations," she said.
The agency could not ignore its statutory obligation to report Iran to the UN Security Council, she added.
But the BBC's Bethany Bell in Vienna says such a move is highly unlikely at present.
It would seriously undermine diplomatic efforts to persuade Iran to give up its enrichment programme, she says.
France, the UK and Germany are trying to persuade Iran to make its freeze on enrichment permanent, in exchange for trade and technology benefits.
The US has also said it is considering offering economic incentives to Iran in exchange for it abandoning plans to develop a nuclear weapon.