TEHRAN - Under pressure to meet a UN deadline, Iran began detailed negotiations yesterday on the signing of an additional protocol to the Nuclear Nonproliferation Treaty that would grant UN inspectors the right of unfettered access.

"The talks may take several days, [but] I'm optimistic that [we] will reach an agreement," said Ali Akbar Salehi, Iran's representative to the International Atomic Energy Agency.

The IAEA, a UN agency, has set a deadline of Oct. 31 for Iran to prove it has no secret program for producing nuclear weapons. If the IAEA finds that Iran has failed to respond satisfactorily, it is expected to refer the matter to the UN Security Council, which could lead to the imposition of sanctions.

The United States strongly suspects Iran does have a secret nuclear weapons program. Iran insists its nuclear facilities are only for generating electricity.

Yesterday's talks follow a one-day visit to Tehran this week by Mohammed ElBaradei, the head of the IAEA, who said his organization still had "outstanding issues" to resolve with Iran.

ElBaradei said in Tehran on Thursday that Iran had promised greater access for IAEA inspectors. He said Iran had allowed inspectors to visit one military site and that there could be expanded reviews of both military and civilian facilities in the future.

The IAEA has urged Iran for months to sign the additional protocol to the Nuclear Nonproliferation Treaty that would give IAEA inspectors access to any site they deem fit without notice.

Under Iran's existing agreement to the treaty, the country is not required to allow IAEA inspectors to visit nonnuclear sites, including military installations.