A week before deadline, Iran Thursday delivered what it says is a complete declaration of its past nuclear activity to the International Atomic Energy Agency.
The IAEA says Iranian envoy Ali Akbar Salehi handed over files to the agency Thursday to document the precise nature of Tehran's nuclear program.
The United States suspects Iran is secretly planning to build nuclear weapons, but Iran maintains its nuclear ambitions are purely peaceful.
The IAEA says an official letter from Iran, confirming that it will sign a legal agreement allowing for tougher inspections, is expected in the next few days.
IAEA spokeswoman, Melissa Fleming, says the documents must provide information on Iran's enrichment program.
"Their enrichment program has come a long way and it has raised a lot of questions about how they got there," she said. "So there are a lot of questions there that remain to be answered as well as this question of why we found traces of highly enriched uranium at two sites."
Iran says particles of weapons grade uranium found at the sites came from imported equipment bought on the black market. But the IAEA has told Iran it needs to know names of the middlemen involved in the transactions.
The agency will sift through the documents in the coming days to see if Iran has provided such information.
Iran has in the meantime suspended its uranium enrichment program in accordance with a resolution passed by the IAEA board of governors last month. U.N. inspectors will visit locations in Iran and take environmental samples until the end of October.
The IAEA board of governors will meet at the end of November to assess whether Iran's nuclear declaration is complete and accurate. Omissions or discrepancies could result in Iranian officials coming before the U.N. Security Council where Iran could face sanctions.