The International Atomic Energy Agency (IAEA) on Wednesday acknowledged that the visit to Iran by inspectors probing its suspected nuclear weapons program failed to achieve a breakthrough, as Tehran denied them access to a key site and warned of a pre-emptive strike against any nation that threatens Iran.

“Intensive efforts were made to reach agreement on a document facilitating the clarification of unresolved issues in connection with Iran’s nuclear program,” the U.N. nuclear watchdog agency said in a statement. “Unfortunately, agreement was not reached on this document.”

The U.N. inspectors had requested access to the Parchin military site, near Tehran, both during this week’s current two-day visit and on a previous trip in late January. The agency believes explosives testing was carried out at the site, but Iran “did not grant permission,” the statement 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.”

The statement did not say whether another such visit was planned.

As the two-day IAEA visit wound down, Iranian officials sought to cast it in a positive light, with Foreign Ministry spokesman Ramin Mehmanparast telling reporters that “cooperation with the agency continues and is at its best level.”

Beyond differing with that view, the language of the IAEA communique clearly - if indirectly - blamed Tehran for the lack of progress.

The statement also said no agreement was reached on how to begin “clarification of unresolved issues in connection with Iran’s nuclear program, particularly those relating to possible military dimensions.”

The visit was just the latest sign of Iranian resolve to continue hard-line resistance in the face of international pressure to curb its nuclear activities, despite sanctions and U.S. and Israeli warnings of possible military action should diplomacy fail.

Iran flexed its muscles once more just hours before the IAEA team left, with Gen. Mohammed Hejazi, who heads the military’s logistical wing, warning that Iran would “not wait for enemies to take action against us.”

“We will use all our means to protect our national interests,” he told the semiofficial Fars news agency.

Hejazi did not mention Israel or the U.S. by name but his statement comes on the heels of recent reports of an imminent Israeli or U.S. military strike on Iran’s nuclear facilities. The New York Times pointed out on Tuesday that rising internal tension in Iran among different political factions makes it difficult to assess the direction the regime is taking, although according to the report “the message presents a new aggressive level in Iran’s rhetoric.”

His comments followed Iran’s announcement of war games to practice protecting nuclear and other sensitive sites, the latest military maneuver viewed as a message to the U.S. and Israel that the Islamic Republic is ready both to defend itself and to retaliate against an armed strike.

The official news agency IRNA said the four-day air-defense war games, dubbed “Sarallah,” or “God’s Revenge,” were taking place in the south of the country and involve anti-aircraft batteries, radar, and warplanes. The drill will be held over 73,000 square miles (190,000 square kilometers) near the port of Bushehr, the site of an Iranian nuclear power plant.

Iran has held multiple air, land, and sea maneuvers in recent months as tensions increase, while at the same time continuing to deny any interest in nuclear weapons. It asserts that allegations of secret work on developing such arms are based on fabricated U.S. and Israeli intelligence.

But Yukio Amano, the IAEA chief, outlined his concerns in a 13-page summary late last year listing clandestine activities that he said can either be used in civilian or military nuclear programs, or “are specific to nuclear weapons.”

Among these were indications that Iran has conducted high-explosives testing to set off a nuclear charge at Parchin - the site the agency said Wednesday that the IAEA team was not allowed to visit.

Other suspicions include computer modeling of a core of a nuclear warhead and alleged preparatory work for a nuclear weapons test and development of a nuclear payload for Iran’s Shahab 3 intermediate-range missile - a weapon that could reach Israel.

The IAEA team had hoped to talk to key Iranian scientists suspected of working on the alleged weapons program, break down opposition to their plans to inspect documents related to nuclear work and secure commitments from Iranian authorities to allow future visits.

Iran’s envoy to the IAEA, Ali Asghar Soltanieh, told the country’s ISNA news agency that Tehran expected to hold more talks with the U.N. agency and Iranian officials reportedly said the U.N. team was in Iran only for talks, not to visit nuclear facilities.

Beyond denying any covert work on nuclear arms, Iran also insists concerns that it will turn its uranium enrichment program to making fissile warhead material are unfounded, saying it is enriching uranium only to make nuclear fuel for peaceful purposes such as producing energy.

But because of weapons fears, the U.N. Security Council has imposed sanctions on Tehran in a failed attempt to force it to stop enrichment. More recently, the U.S., the European Union and other Western allies have either tightened their own sanctions or rapidly put new penalties in place striking at the heart of Iran’s oil exports lifeline and its financial system.

Tehran’s expanding enrichment activities at its plant at Fordo, near the city of Qom, are of particular concern for Israel - which has warned it would not let Iran develop nuclear arms - because it is fortified and possibly resistant to attack.

Diplomats last week said Iran is poised to install thousands of new-generation centrifuges at the cavernous facility. That would mean Iran would be able to enrich to weapons-grade level much more quickly and efficiently than with its current machines.

Despite concerns over Iran’s ongoing refusal to comply with international demands to halt its nuclear program, the White House believes there is still time for diplomacy. “Israel and the United States share the same objective, which is to prevent Iran from acquiring a nuclear weapon,” White House spokesman Jay Carney said when asked about a weekend visit to Israel by U.S. National Security Adviser Tom Donilon. “There is time and space for diplomacy to work, for the effect of sanctions to result in a change of Iranian behavior.”

Israel, meanwhile, has urged the U.S. to take immediate action to halt Iran’s nuclear program. In a meeting between Donilon, Defense Minister Ehud Barak and Chief of General Staff Lt. Gen. Benny Gantz, the Israeli officials made it clear that as long as Iran does not terminate its nuclear program, action must be taken at once to stop it from progressing any further.

Israeli government officials believe Iran is using diversionary tactics - such as agreeing to talks with Western countries - to stall for time and allow it to advance its nuclear projects.

Commenting on remarks over the weekend by U.S. Chairman of the Joint Chiefs of Staff Gen. Martin Dempsey in which he called Iran “a rational actor,” Senator John McCain (R-Ariz.) said, “I admire General Dempsey, but I don’t think it is helpful to say that Iran is a rational actor given their behavior. He who denies the Holocaust, as the Iranian president has, plots to kill the Saudi ambassador in Washington, and behaves the same way with his own people, does not seem rational to me.”

McCain, who is currently visiting Israel, added, “There should be no daylight between America and Israel in our assessment of the threat [from Iran]. Unfortunately there clearly is some.”

Deputy Foreign Minister Danny Ayalon on Tuesday said there is no crisis developing between Jerusalem and Washington on the Iran issue, and that understandings between them are in fact broadening, according to Israel Radio. Prime Minister Benjamin Netanyahu is scheduled to meet U.S. President Barack Obama in Washington next month to discuss the Iranian threat.

Meanwhile, Japan, China and India are expected to announce a reduction of Iranian crude oil imports. According to Japanese media reports, Japan and the U.S. are formulating an agreement according to which Japan will reduce its crude oil imports from Iran by 34,430 barrels per day, which constitutes 11% of Japan’s overall oil imports.

China and India - Iran’s largest clients, who together purchase 45% of Iran’s total oil exports - are also expected to announce reductions in their imports of Iranian oil due to the increasing difficulty of doing business with Iran, despite the fact that they have not joined the U.S. and EU in imposing sanctions on the Islamic Republic. China is expected to reduce its consumption of Iranian oil by 14%.