The UN nuclear watchdog has expressed disappointment after a two-day visit to Iran by a team of UN nuclear experts.
In a statement, the head of the International Atomic Energy Agency said Tehran had refused access to a military complex at Parchin.
Yukiya Amano also said there was no agreement reached on how to clarify questions about Iran's nuclear program.
IAEA inspectors last visited Parchin in 2005, but not all areas of interest within the complex.
Correspondents say Parchin was highlighted in the IAEA's latest report on Iran late last year, which said some of Iran's nuclear activities could only have a military application.
Earlier, Iran's envoy to the IAEA, Ali Asghar Soltahieh, told the country's ISNA news agency that Tehran expected more talks with the UN agency.
The IAEA, however, said no further discussions were planned.
Just hours before the IAEA was to depart Iran, the deputy head of the Iran's armed forces was quoted as saying his nation will "not wait for enemies to take action against us."
Mohammad Hejazi told the Fars news agency Iran "will use all our means to protect our national interests."
The IAEA team had arrived in Tehran as Iran launched four days of air defense exercises in the south of the country.
The exercises, dubbed "Sarollah," or "God's Revenge,"are taking place near the port of Bushehr, the site of Iran's sole nuclear power plant.
Iran has held similar exercises as tensions ratchet up with the West.
Iran has repeatedly denied Western accusations it is trying to secretly develop nuclear weapons.
Tehran claims its nuclear program is only for energy production and cancer research.