A top Iranian general has warned that it will pre-emptively strike anyone who threatens it.
The statement by General Mohammed Hejazi continues the defiant tone Tehran has taken in its confrontation with Western countries that claim it is developing nuclear weapons.
Iran says its nuclear programme is for peaceful purposes.
"We do not wait for enemies to take action against us," said Hejazi, according to the Fars news agency. "We will use all our means to protect our national interests."
Hejazi heads the military's logistical wing.
The US and Israel have not ruled out strikes against Iranian nuclear facilities.
Iran also said that a visiting UN team did not plan to inspect the country's nuclear facilities and will only hold talks with officials in Tehran.
The statement cast doubt on how well UN inspectors can gauge whether Iran is moving ahead with its suspected pursuit of nuclear weapons.
The visit by the International Atomic Energy Agency team, which started on Monday, is the second in less than a month.
Foreign Ministry spokesman Ramin Mehmanparast said the visiting IAEA team was made up of experts, not inspectors. He told reporters that the IAEA team was holding discussions in Tehran to prepare for future cooperation between Iran and the UN watchdog. He said this co-operation is at its "best" level.
"The (title) of the members of the visiting delegation is not 'inspectors.' This is an expert delegation. The purpose of visit is not inspection," said Mehmanparast. "The aim is to negotiate about co-operation between Iran and the agency and to set a framework for a continuation of the talks."
Visits to Iranian nuclear sites were not part of the IAEA visit three weeks ago.
But on Monday, Iranian state radio said the UN team had asked to visit the Parchin military complex outside Tehran - a known, conventional arms facility that has been suspected of making secret weapons - and to meet Iranian nuclear scientists involved in the country's controversial programme.
The visit comes as Iran carries out air defence war games to practice protecting nuclear and other sensitive sites.