The UN nuclear watchdog says Iran has supplied transparent data on its past nuclear activities but adds it has limited knowledge of its current work.
Mr ElBaradei has said Iran is years away from making a nuclear bomb
The IAEA also found in a report that Tehran was still enriching uranium in defiance of the UN Security Council.
Iran said the report was a clean bill of health but the US said it showed Tehran was not co-operating.
The BBC's Jon Leyne says Iran probably has done enough to fend off any new UN sanctions and has deferred the crisis.
The International Atomic Energy Agency (IAEA) agreed a deal in August with Iran to answer outstanding questions as part of a four-year probe into its nuclear drive.
The confidential IAEA report will form the basis for deliberations when representatives of the five permanent members of the UN Security Council, along with Germany, meet on Monday in Brussels.
The BBC's Bethany Bell in Vienna says that while a number of questions about Iran's past nuclear work have been answered, the report says the IAEA's knowledge about Tehran's current nuclear programme is diminishing.
The report, a copy of which was obtained by the BBC, found Tehran had been operating 3,000 centrifuges, the machines used to enrich uranium, at its plant at Natanz.
"Contrary to the decisions of the Security Council, Iran has not suspended its enrichment related activities," the document says.
But the IAEA also noted the answers Iran had given about the history of its centrifuge programme were consistent with the agency's own findings.
The report by IAEA Director-General Mohamed ElBaradei praised Iran for making progress in responding to questions about its past nuclear activities.
"Iran has provided sufficient access to individuals and has responded in a timely manner to questions and provided clarifications and amplifications on issues raised in the context of the work plan," the report said.
A senior UN official said this was a significant step forward.
However, the report said Iran's co-operation with the IAEA had been "reactive" rather than "pro-active" and that the IAEA was continuing to check whether Iran's declarations were complete.
On Tuesday, diplomats said Iran had given the IAEA a document containing design information that could be used for parts of a nuclear weapon. The IAEA had been asking Iran for the document since 2005.
Western powers are concerned because, while enriched uranium is used as fuel for nuclear reactors, highly enriched uranium can also be used to make nuclear bombs.
Tehran has argued that it needs nuclear power and insists its intentions are entirely peaceful.
At a Tehran news conference held after the report was given to the IAEA board and the Security Council, Iran's new chief nuclear negotiator welcomed the findings.
Saeed Jalili said: "For those who had doubts about the Iranian nuclear programme, the report is very clear and indicates that the basis upon which the nuclear case was referred to the Security Council has collapsed."
However, the US said the IAEA confirmation of Iran's expanding uranium enrichment programme backed up their argument that Tehran was continuing to defy world demands.
White House spokeswoman Dana Perino said: "The United States will work with our partners on the UN Security Council and Germany as we move towards a third set of Security Council sanctions."