Iranian state television has broadcast unprecedented footage of a deep underground tunnel packed with missiles and launcher units, which officials said could be used if "enemies make a mistake."
The pictures were released on October 14, just days after Iran tested a new long-range missile that the United States said breached UN restrictions.
Washington has said, 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 aims to restrict Iran's path to a nuclear weapon.
Iran is prohibited, however, from any activities related to ballistic missiles under an older UN Security Council resolution, and a newer one -- not in effect yet -- on implementing that July nuclear deal.
Iranian officials have said the nuclear agreement reached with world powers will not affect its military forces, particularly its ballistic-missile program.
Under the July 14 nuclear agreement, sanctions against Iran will be gradually lifted in return for Tehran imposing curbs on nuclear activities, which the West suspects are aimed at making an atomic bomb.
The missile launch and underground footage followed pressure from lawmakers to prove the military had not been weakened by the deal.
The tunnel, hundreds of meters long and about 10 meters high, was filled with missiles and hardware.
Brigadier General Amir Ali Hajizadeh, commander of the Islamic Revolutionary Guards Corps' aerospace division, said numerous such tunnels exist across the country at a depth of 500 meters.
"The Islamic republic's long-range missile bases are stationed and ready under the high mountains in all the country's provinces and cities," he said.
The commander said the missiles were ready to be launched from all over Iran, on the order of "the supreme commander in chief," Ayatollah Ali Khamenei.
"This is a sample of our massive missile bases," he said, adding that "a new and advanced generation of long-range liquid and solid-fuel missiles" would start to replace the current weapons next year.
The commander seemed to suggest the show of strength was in response to Western powers, especially the United States, which has said the military option against Iran remains on the table.
"Those who pin hope on options on the table should only have a look at the Islamic republic's army options under the table," he said.
Hajizadeh said Iran would not start any war but "if enemies make a mistake, missile bases will erupt like a volcano from the depth of earth."
U.S. Secretary of Defense Ash Carter told U.S. lawmakers recently that the nuclear agreement with Iran would not limit the United States' ability to respond with military force if needed.
With reporting by AFP and AP