With a key deadline approaching, the head of the U.N. nuclear agency is leaving for Tehran Saturday for high-level meetings as he tries to accelerate his probe of allegations that Iran worked in the past on nuclear weapons.

Diplomats had said Friday that Yukiya Amano of the U.N.'s International Atomic Energy Agency was planning such a trip. Confirming Amano's trip, IAEA spokesman Fredrik Dahl said that Amano would arrive Sunday for meetings aimed at "clarifications of past and present outstanding issues" linked to the agency's probe.

The diplomats say Amano plans to push for long-delayed interviews with Iranian scientists linked to alleged experiments as well as to discuss a planned inspection of Parchin. The agency has identified that site, southeast of Tehran, as where some of the suspected work took place.

The diplomats, who are accredited to the IAEA, demanded anonymity because they are not authorized to discuss Amano's agenda.

The trip is significant. Amano is traveling less than a month before an Oct. 15 deadline to gather information on allegations that Iran tried to build atomic weapons.

A final U.N. assessment is due in December, and that will feed into the larger July 14 nuclear deal between Iran and six world powers, helping to determine whether sanctions on Iran will be lifted.

The interviews and the Parchin inspection are crucial to IAEA's goal of wrapping up more than a decade of IAEA efforts to probe the allegations.

Iran denies any work on — or interest in — nuclear weapons. It says IAEA suspicions are based on false intelligence from the United States, Israel and other adversaries. In refusing access to scientists the agency is interested in, Iran cites past assassinations of several experts it says worked on peaceful nuclear programs.

After allowing a previous visit to Parchin that the IAEA now says went to a false area unconnected to the alleged experiments, Tehran has kept the IAEA away from the sprawling military site southeast of Tehran. The agency believes Iranian scientists experimented there with explosives meant to set off a nuclear charge.