Iran has agreed to clarify all outstanding questions over its past nuclear activities within a month, the UN nuclear watchdog has announced.
ElBaradei has failed to persuade Iran to stop uranium enrichment
The IAEA made the announcement after talks in Tehran held by the agency's head, Mohamed ElBaradei.
A senior official from Iran's atomic energy agency confirmed the agreement, saying Iran has nothing to hide.
Western countries fear Iran is refusing to suspend uranium enrichment because it wants to produce a nuclear weapon.
Tehran denies this, insisting the programme is solely to generate electricity.
An IAEA spokeswoman said Mr ElBaradei had also received information on Iran's "new generation of centrifuges".
The announcement by the International Atomic Energy Agency (IAEA) came after Mohamed ElBaradei's two-day visit to Iran, during which he met top officials including President Mahmoud Ahmadinejad.
He has been trying to resolve various issues about the history of Iran's nuclear programme.
Iran insists its nuclear programme is only to provide energy
The deputy head of Iran's atomic energy agency, Mohammed Saeedi, said his country would "respond within the space of four weeks to the remaining questions so that the IAEA can make a transparent report on the Iranian nuclear programme.
"The Islamic Republic of Iran has nothing to hide, and that's why it does not fear answering the remaining questions. I am optimistic."
But the BBC's Jon Leyne in Tehran says that even if Iran does provide all the answers, this is not going to solve this crisis.
The West is more concerned about Iran's current activities than the history, our correspondent says.
Washington said the agreement does not go far enough and that Iran should stop enriching uranium.
"Answering questions about their past nuclear activities is a step, but they still need to suspend their enrichment and reprocessing activity," said White House spokesman Gordon Johndroe.
The fear is that the uranium enrichment programme could be used to make a nuclear bomb, as US President George W Bush has stressed during his current tour of the region.
In a speech in Abu Dhabi on Sunday, he said Iran was the "world's leading state sponsor of terrorism".
Mr ElBaradei will also be looking at how to monitor Iran's future nuclear activities.
But so far he has made little progress in persuading Iran to stop the controversial process of enriching uranium.
The US is currently pushing for a third round of UN sanctions against Iran over its refusal to stop enriching uranium, a process which can be used both to make atomic fuel and a bomb.
Washington has said it believes Iran is planning to build a nuclear bomb.
Its campaign for tougher sanctions lost some steam when a US intelligence report last month suggested Iran had abandoned its nuclear weapons programme in 2003.