The United Nations nuclear watchdog says it has received documents from Iran clarifying its past nuclear activities.
ElBaradei says the IAEA will try to piece together Iran's nuclear history
The head of the International Atomic Energy Agency (IAEA), Mohamed ElBaradei, acknowledged receiving the files from Iranian envoy Ali Akbar Salehi on Thursday.
"I was assured that the report I got today is a comprehensive and accurate declaration," Mr ElBaradei said, adding that his staff would immediately begin studying the material.
Iran handed in the declaration eight days ahead of a UN deadline for the country to prove it is not developing nuclear weapons.
"It is a large set of documents," said Mr ElBaradei. "We obviously have to start our verification activities [but] it is going to take us time to go through all these documents and reconstruct the full history of the programme."
Mr Salehi, Iran's ambassador to the IAEA, declined to give any details about the files but said they "fully disclosed" Iran's "past peaceful activities in the nuclear field".
"The important thing to note is that Iran had to do some of
its activities very discreetly because of the sanctions that have been imposed on Iran for the past 25 years," Mr Salehi added.
Following Tehran's decision to agree to tougher international inspections, the country's supreme leader, Ayatollah Ali Khamenei, said Iran did not intend to build nuclear arms.
"We have always said we have no need of nuclear weapons because the possession of such arms does not signify power," he said in what is believed to be his first public pronouncement on the issue.
Th ayatollah said claims that Iran was seeking nuclear weapons were part of a plot "to stop Iran from having nuclear science and technology and to keep Iran dependent on Western technology".
The United States has spearheaded international demands for snap inspections of Iran's nuclear sites.
President George W Bush thanked the foreign ministers of Germany, France and Britain who mediated the deal "for taking a very strong universal message to the Iranians that they should disarm".
"It looks like they're accepting the demands of the free world, and now it's up to them to prove it," Mr Bush said in Indonesia.
The decision to comply was reached by Iran's hardliners, says the BBC's Tehran correspondent Jim Muir, and some are unhappy about it.
Iranian analysts have not ruled out the possibility that disgruntled hardliners might try to stage some spectacular action to discredit the course the regime has decided to take, our correspondent says.
The IAEA wants clarification on how traces of highly enriched uranium came to be found at two of Iran's facilities.
Tehran has said the particles were contamination on imported components brought from middle men in the 1980s.
But the UN agency wants detailed information to dispel suspicions that Iran may have been testing centrifuges with enriched uranium, says our correspondent.
If Tehran had not satisfied the agency that it had come completely clean by the deadline, it could have faced referral to the UN Security Council and possible sanctions
In that situation the agreement won by the three European foreign ministers in Tehran on Tuesday would have counted for nothing, our correspondent says.