Iran is still failing to provide answers in a probe into its nuclear activities, and is unlikely to do so before a November 24 deadline for a deal with world powers, the UN atomic watchdog said Friday.

"Iran has not provided any explanations" on two issues that Tehran had undertaken to clarify by August 25, the International Atomic Energy Agency said in a new quarterly report.

Iran and the IAEA have agreed to a "technical meeting to further discuss the two outstanding practical measures ... but not before November 24," said the report, not yet public but seen by AFP.

"There is no progress, basically," a diplomat familiar with the IAEA's probe said.

The IAEA conducts regular inspections of Iran's nuclear facilities but it also wants Tehran to address allegations of suspected covert efforts, mostly in the past, to develop nuclear weapons.

Iran, which rejects the accusations, agreed in May to provide the IAEA information on two out of around a dozen areas of suspicious alleged activity by the August deadline.

Iran and six world powers are seeking a separate landmark deal by November 24 but this concerns Iran's current and declared activities, most notably its uranium enrichment facilities.

But the US envoy to the IAEA, Laura Kennedy, said in September that the watchdog's allegations "must be addressed as part of any comprehensive" wider deal between Iran and world powers.

"Only when this happens will it be possible to have confidence that Iran's nuclear programme is and will remain exclusively peaceful," she told reporters.

But Iran rejects the IAEA's claims as being based on faulty intelligence -- some analysts are also critical -- and Tehran's envoy to the watchdog on Friday questioned the new report.

"The fact that the agency claims that Iran's explanation does not enable the agency to clarify the outstanding practical measures, is a wrong reflection of reality," Reza Najafi told the IRNA news agency.

He said the IAEA "too has not been able to provide explanations to prove its documents and information are not fake. That's why the meetings will continue," he said.

On Friday senior negotiators from the six world powers gathered in Vienna, kicking off a flurry of final meetings before the November 24 deadline.

On Sunday and Monday US Secretary of State John Kerry and Iranian counterpart Mohammad Javad Zarif will meet in Oman together with former EU foreign policy chief Catherine Ashton.

Ashton, who will continue chairing the negotiations until the deadline, will then on Tuesday chair another meeting of political directors from the P5+1 powers, also in Muscat.

The grand finale then starts in the Austrian capital on November 18 when the six powers and Iran begin a final round, likely including Kerry and other foreign ministers at the end.