VIENNA: A visit to Iran by United Nations (UN) inspectors tasked to probe the country’s suspected nuclear weapons activities failed to achieve a breakthrough, with Tehran denying access to a key military site, according to the International Atomic Energy Agency (IAEA).

“Intensive efforts were made to reach [an] agreement on a document facilitating the clarification of unresolved issues in connection with Iran’s nuclear program,” the IAEA said in a statement on Wednesday.

“Unfortunately, [an] agreement was not reached on this document,” it added.

The team requested access both during this visit and during a first trip in late January to the Parchin military site, near Tehran, where it believes that explosives testing was carried out, but Iran “did not grant permission,” the UN agency said.

“It is disappointing that Iran did not accept our request to visit Parchin during the first or second meetings,” IAEA Director General Yukiya Amano said in the statement.

“We engaged in a constructive spirit, but no agreement was reached,” he added.

The statement gave no further details and did not say whether another visit was planned.

Iran’s envoy to the IAEA, Ali Asghar Soltanieh, was quoted by the Iranian Students’ News Agency as saying that the talks had been intensive and covered “cooperation and mutual understanding between Iran and the IAEA.”

“These negotiations will continue in the future,” Soltanieh said.

The high-ranking IAEA team led by Herman Nackaerts, the Vienna-based agency’s Belgian chief inspector and his Argentine deputy Rafael Grossi, was due back in Vienna later on Wednesday.

The visit, the nuclear agency had said, was aimed at clarifying all “outstanding substantive issues” surrounding Tehran’s nuclear program, in particular what it called “possible military dimensions.”

The trip was also seen as an important precursor to a possible resumption of talks between Iran and the 5+1 powers—the United States, China, Russia, France, Britain and Germany—which broke down in Turkey 13 months ago.

Mark Hibbs, an analyst at the Carnegie Endowment for International Peace, said before the visit that it represented “a last chance for Iran to make a significant gesture.”

A watershed report from the IAEA in November said that Iran had carried out activities in a number of areas “relevant to producing” a nuclear weapon.

The report added that its information suggested that Iran tested in “a large . . . containment vessel” at Parchin high explosives in experiments thought to be relevant to designing a ballistic missile payload.

Since the report’s publication, the United States and the European Union have ramped up sanctions on Iran’s oil sector, and speculation has grown that Iran’s arch-rival Israel might launch air strikes, possibly even this year.