Yielding to international demands for it to prove it is not developing nuclear weapons, Iran agreed to allow tougher inspections of its nuclear sites and to halt uranium enrichment.
ElBaradei said in a statement he "hopes and expects that in the next few days Iran will deliver to the IAEA (International Atomic Energy Agency) a complete declaration of all its past nuclear activities and an official notification of its readiness to conclude an additional protocol" to the nuclear Non-Proliferation Treaty (NPT) on the snap inspections.
The IAEA chief described the outcome of talks in Tehran as "an encouraging sign toward clarifying all aspects of Iran's past nuclear program and regulating its future activities through verification."
ElBaradei visited Tehran last week to press for Iran's cooperation ahead of a October 31 deadline set by the agency for the Islamic republic to prove it is not secretly trying to develop nuclear weapons.
A diplomat close to the IAEA said Iran was expected to hand over the information by the end of the week.
He said this would be "a lot of written material" given to IAEA inspectors in Tehran, including records of what Iran has purchased and from where, how it tested and did development of centrifuges that can be used to enrich uranium and a history of its scientific experiments and development.
Iran claims that traces of highly enriched uranium found at two sites by the IAEA were from contaminated imported equipment, and not from its own enrichment activities.
Enriched uranium can be used in nuclear reactors but highly-enriched uranium is a key ingredient to produce nuclear weapons.
The IAEA has asked Iran to provide proof showing which countries the equipment came.
The diplomat said that "what's interesting about the Iranians' declaration today is that it refers to their decision to engage in full cooperation to verify and correct any possible failures and deficiencies.
"This seems to be an implied readiness to reveal or confess to activities that hadn't been reported to us before," he said.
But a Western diplomat said he remained pessimistic about Iranian compliance.
"It's not as if the Iranians haven't promised many times to sign the additional protocol," he said.
He said that signing the protocol would not affect the October 31 deadline since it would still have to be ratified, which is a lengthy process.
"We don't see any evidence that cooperation has been anything but halting. We have to wait and see whether the Iranian actions live up to their promises," the Western diplomat said.
He said he thought the IAEA would after October 31 find that the Iranians had not supplied all the information requested and would still have to declare the Islamic Republic in non-compliance, a step which would send the issue to the UN Security Council for possible sanctions.
He said that Russia, which is building a nuclear reactor in Iran, would not veto UN sanctions against Iran.
But Moscow would object to a "quid-pro-quo" rewarding of Iran for cooperation by giving it nuclear fuel, since this would come from Britain or France, and deny them money they would have earned from providing fuel, he said.
A diplomat said the British-French-German offer that hinted at supplying civilian nuclear technology and possible nuclear fuel in return for Iranian cooperation and a halt to their own enrichment activities had clearly been a major factor in Iran's promises Tuesday.
"You have to show the Iranians why it is in their interest" to cooperate, the diplomat said.