"At first glance, it looks comprehensive," Mohamed ElBaradei told reporters after meeting with Canadian Foreign Minister Bill Graham.
"We have our inspectors in Iran now, verifying that declaration," the International Atomic Energy Agency (IAEA) chief added. "I think we are making good progress."
The IAEA had given Iran until Friday to provide full disclosure of its nuclear program and to prove to the UN nuclear watchdog it is not secretly making atomic weapons.
Iran seized the diplomatic initiative when it delivered a report to the IAEA on October 23 that it said answered all the agency's questions, one week ahead of the deadline.
The IAEA has been investigating Iran's nuclear program since February but Tehran only issued the report after reaching an agreement with three leading EU foreign ministers.
"Iran has been more forthcoming than recently" on the nuclear issue, Graham told reporters, but also warned "there are a lot of very technical questions that have to be asked."
Although nothing definitive will happen Friday, the UN agency is to begin writing a report on Iranian compliance, with the matter to be considered at an IAEA board of governors meeting in Vienna on November 20.
At stake is whether the IAEA judges Iran to be in non-compliance with the nuclear Non-Proliferation Treaty (NPT) and sends the issue to the UN Security Council, which could then impose sanctions on the country.
The foreign ministers of Britain, France and Germany visited Tehran earlier this month to persuade Iran to come clean on its nuclear program and allow tougher inspections of nuclear sites.
Iran has promised to suspend uranium enrichment that can produce highly enriched uranium useable for nuclear fuel but also to make atomic bombs.
It is currently working through the modalities of suspending uranium enrichment -- a key IAEA demand which Iran's clerical leaders agreed to meet during the visit by Britain's Jack Straw, Dominique de Villepin of France and Germany's Joschka Fischer.
The United States said Wednesday that Washington expects Iran to accept increased inspections of its nuclear installations and to meet its international commitments.
"We've said that there are three key aspects involved here for Iran to meet its obligations," said White House spokesman Scott McClellan. "They need to implement -- sign and implement the additional protocol; cooperate fully with the IAEA; and once and for all, suspend its uranium enrichment and reprocessing activities."
Iran has said it will sign the additional protocol to the Non-Proliferation Treaty allowing virtually unannounced inspections of nuclear sites.