The head of the Iranian delegation, Ali Akbar Salehi, said he expected the Tehran talks to last for several days but added that he was optimistic agreement could be reached on Iran's implementation of an additional protocol to the nuclear Non-Proliferation Treaty.
He said he did not exclude a settlement before the October 31 deadline set by the IAEA in the face of growing international concern about Iran's nuclear activities, but added that Iran did not feel bound by that timetable.
"Everything is possible," he said. "We have never considered any dateline, we proceed in accordance with our pace and our interests."
Signature of the protocol would open up suspect sites across Iran 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 of Iran last month amid accusations it is concealing nuclear weapons development behind its civil energy programme.
Archfoe the United States has said the Islamic regime should sign without prior negotiations, but Iranian officials insist talks are essential to protect the country's legitimate national security and scientific interests.
At an Islamic summit in Malaysia Friday, reformist President Mohammad Khatami said he saw no reason why Iran could not come to an accommodation with the UN nuclear watchdog.
"We never said we would not sign the protocol and cooperate with the IAEA," he said.
The IAEA has also demanded answers about other concerns, notably evidence that Iran has been engaged in producing highly-enriched uranium.
Iran insists that two samples taken by IAEA inspectors which showed traces of the weapons-grade material were the result of contamination on imported equipment.