In a rare moment of openness, Iran on Wednesday broadcast pictures from The Islamic Revolution Guards Corps (IRGC) Aerospace Force of a tunnel reportedly dug some 1,640 feet (500 meters) under a mountain.
The release of this footage comes just a few days after state media reported that Iran had test-fired new generation long-range ballistic missiles.
Based on information the administration has so far, the test appears to be in violation of U.N. Security Council Resolution 1929, which stipulates that Iran cannot engage in any activities related to ballistic missiles.
The U.S. official emphasized, however, that the test is not in violation of the nuclear agreement reached in July between Iran, the United States and five other world powers because that accord is focused on restricting Iran's path to a nuclear weapon.
A newer U.N. Security Council resolution, number 2231, implementing the deal and banning Iran from engaging in activities related to ballistic missiles designed to carry nuclear warheads is not yet in effect.
Iran is completely overhauling its missile technology, replacing the current stockpile with newer weapons, a senior general told state media.
"As of next year, a new and advanced generation of long-range liquid and solid fuel missiles will replace the current products," said Brigadier General Amir Ali Hajizadeh.
"The missiles in various ranges are mounted on the launchers in all bases and (are) ready to be launched."
The underground facility shown on television was only one of "numerous missile bases" scattered across the country, according to Hajizadeh.
Earlier this month in a speech at a university in Tehran, Hajizadeh said that all U.S. military bases in the Middle East were within range of Iranian missiles.
The revealing of the underground bases comes in the wake of a major deal reached by Iran and the so-called P5+1 group of nations -- the U.S., U.K., Russia, China, France and Germany -- over its nuclear program.
Under the deal, international sanctions on Iran will be lifted in return for restrictions on its nuclear program aimed at preventing it from being able to develop an atomic bomb.
Iran is a major regional military power and Revolutionary Guards forces have been active in Syria, working to prop up the regime of close Tehran ally Bashar al-Assad with military aid and advisers.
CNN's Jim Sciutto, Tim Hume, Hamdi Alkhshali and James Griffiths contributed to this report.