Iran's representative to the IAEA, Ali Akbar Salehi, said Iran "now has a more positive stance" towards the additional protocol of the Non-Proliferation Treaty (NPT) following two days of "intensive negotiations".
"We found a mutual understanding. We had indicated some ambiguities and, in the course of our discussions, the ambiguities were removed," he said, adding that "our observations were taken into consideration".
Salehi said it was now up to the Iranian leadership to decide whether to sign the additional protocol, a key demand of the Vienna-based UN nuclear watchdog.
"I will remit my conclusions to my superiors, and we will have to wait to see what their decision will be."
He said he expected them to decide in "a matter of days or weeks" whether to accept the new understanding or seek further talks.
If Iran joins the 80 other signatories of the additional protocol, its nuclear facilities will be liable to snap inspections by the IAEA.
Implementation of the protocol, even before its formal signature, is one of a series of demands the nuclear watchdog made last month amid accusations Iran is concealing nuclear weapons development behind its civil energy programme.
Iran denies that it is developing nuclear weapons, but the IAEA says its inspectors need the extra powers provided by the additional protocol to fully verify and accurately report on Iran's nuclear programme.
While Iran has never ruled out signing the additional protocol, it has expressed concern that giving the UN watchdog access to its facilities -- many of them sensitive and key to national security -- would represent a surrender of sovereignty.
Iran's concerns -- which it refers to as "ambiguities" in the protocol -- have been at the centre of this week's talks.
The IAEA also wants Iran to provide a whole raft of additional information about its nuclear programme by an October 31 deadline it set last month.
In particular, the IAEA wants to clarify the source of traces of highly enriched uranium found in samples taken by its inspectors.
Iran insists the traces were the result of contamination on imported equipment, but IAEA director general Mohamed ElBaradei has accused Iran of dragging its feet in providing the necessary information to clear up the issue.
Salehi promised that Iran would "give the IAEA enough information for it to reach a conclusion".