Two days of talks in Iran went nowhere and the frustration of the global nuclear watchdog agency was palpable in the terse statement it issued afterward.

The International Atomic Energy Agency team could not make progress with Iran. Nor was it able to to visit a military base at Parchin, southeast of Tehran before leaving the country Tuesday.

"Intensive efforts were made to reach agreement on a document facilitating the clarification of unresolved issues in connection with Iran's nuclear program, particularly those relating to possible military dimensions," an IAEA statement on the visit read. "Unfortunately, agreement was not reached on this document.

"It is disappointing that Iran did not accept our request to visit Parchin during the first or second meetings," IAEA chief Yukiya Amano said in the statement. "We engaged in a constructive spirit, but no agreement was reached."

The agency's frustration, after two visits to Tehran in the last two months, came through loud and clear, though the Iranians had a different take on the matter.

Ali Asqar Soltaniyeh, Iran's representative to the IAEA, said the Iranian and IAEA experts' recent negotiations involved cooperation and mutual understanding between the two sides, the semi-official Fars news agency reported.

Soltaniyeh also said Iran will hold further talks with the agency over its civilian nuclear energy program, according to Fars.

Iran says it is producing enriched uranium to fuel civilian power plants and has refused international demands to halt its production. But the IAEA said in November that it had information to suggest Iran had carried out some weapons-related research.

According to November's IAEA report, Parchin may have been the site of tests of high explosives that could be used to detonate a nuclear bomb -- experiments the agency called "strong indicators of possible weapon development."

The IAEA said Iran built a large, cylindrical chamber at Parchin in 2000 that was designed to contain the force of up to 70 kilograms (154 pounds) of high explosives. IAEA inspectors visited the site twice in 2005, but did not go to the building now believed to have housed the test chamber, the report states.

"It remains for Iran to explain the rationale behind these activities," the report noted.

The talks come as Iran is under intense pressure to demonstrate that it has no intention of pursuing nuclear weapons. U.S. and European sanctions are crippling its currency, while a new round of sanctions are targeting its crude oil sales, which make up about half of Tehran's revenue.

In the meantime, Israel is making clear it is pondering an attack on Iran's nuclear infrastructure. Israel is widely believed to have nuclear weapons itself, though it has never declared itself a nuclear power and considers Iran an existential threat.

Iran has threatened to cut off the Strait of Hormuz, the only shipping lane out of the oil-rich Persian Gulf, if it is attacked. But last week, it also proposed a resumption of long-stalled talks with European powers and Security Council permanent members aimed at resolving the issue.