Iran's envoy to the UN nuclear watchdog played down prospects for a quick breakthrough in talks on Friday with the agency on a stalled investigation into Tehran's disputed atomic program.

Reza Najafi, Iran's ambassador to the International Atomic Energy Agency, was asked by reporters whether he expected an agreement in discussions due to start with the IAEA at around 10 a.m.

The meeting between Iran and the IAEA will be the first since Hassan Rouhani, a relative moderate, took office as new Iranian president in early August, pledging to try to resolve the Islamic state's nuclear dispute with the West.

It comes after talks between Iran and world powers at the United Nations on Thursday.

"This is the first meeting so nobody I guess should expect that in just (a) one-day meeting we can solve (our) problems," Najafi, who was appointed new Iranian ambassador last month, said.

"We are going to have a first meeting with the agency. We expect to review the existing issues and also exchange views on the ways we can continue our cooperation to resolve all issues."

Iran and the United States held their highest-level substantive talks in a generation at the United Nations, saying the tone was positive but sounding cautious about resolving the standoff.

U.S. Secretary of State John Kerry and Iranian Foreign Minister Mohammad Javad Zarif met after Zarif held wider talks with the United States and other major powers to address Western suspicions that Iran may be trying to develop atomic weapons.

Separately from big power diplomacy to resolve the decade-old dispute that could yet trigger a Middle East war, the IAEA has held 10 rounds of talks with Iran since early 2012 to try to resume a blocked inquiry into suspected atom bomb research.

The talks have so far yielded no results but Western states see Friday's meeting in Vienna as a litmus test of any substantive Iranian shift from its intransigence under Rouhani's hardline conservative predecessor, Mahmoud Ahmadinejad.

Iran denies it is seeking to develop the capability make nuclear weapons, saying its program is a peaceful bid to generate electricity.-Reuters