Details of the final test of the Shahab-3 emerged just two days before the head of a United Nations nuclear watchdog agency is due to arrive in the country.
Foreign Ministry spokesman Hamid Reza Asefi said the test had occurred several weeks ago and that the range of the missile was 1,300 km.
He said the missile would be handed over for operation by the Iranian army.
Revelations about the long distance capabilities of the Shahab, known in English as Shooting Star, were revealed last week in the Israeli Haaretz newspaper, heightening security concerns in the region.
The paper said the Islamic republic’s new eapon, modelled on North Korea's No-Dong and Pakistan's Ghauri-II missile systems, was now capable of reaching Israel, US forces in the Gulf or the Indian subcontinent.
“This is nothing new”, Asefi said. “Apparently the Israelis are a bit late with their information.”
Israel reacted to the news immediately. Government spokesman Avi Pazner said: "We are very concerned, especially since we know that Iran is seeking to acquire the nuclear weapon.
"We informed our American and European friends of our concern . . . the combination of the Shahab-3 and the nuclear weapon would be a very serious threat on the stability of the region," he said.
Iran is under pressure from America to clarify its nuclear ambitions and is part of President George W Bush's so-called Axis of Evil.
US pressure on Iran
The head of the International Atomic Energy Agency (IAEA), Mohammed al-Baradei, will arrive in Iran on Wednesday to press for wider inspections of nuclear facilities.
But Asefi asserted that drawn-out negotiations may be necessary.
Iran has come under massive pressure from the US and later from the European Union and the Group-8 states to sign an additional protocol to the Nuclear non-Proliferation Treaty (NPT).
The additional protocol would allow UN inspectors to make surprise visits to Iran’s nuclear facilities.
Washington accuses Iran of using its civilian nuclear programme as a covert to develop nuclear weapons.
Iran denies the charges, saying its nuclear programme aims at generating electricity to meet the needs of a fast-growing population.