"Iran does not have any plan to build a Shahab-4. Instead we are optimising the Shahab-3," said Hossein Dehqan, a deputy to Defence Minister Ali Shamkhani.
Tehran finalised its testing of the Shahab-3 in June. The missile is thought to be capable of carrying a 1,000 kilogramme (one-ton) warhead at least 1,300 kilometers (800 miles) -- therefore bringing arch-enemy Israel within range.
Shahab is Farsi for "meteor" or "shooting star".
Six Shahab-3 missiles were paraded in Tehran in September during the festivities marking the outbreak of the 1980-88 Iran-Iraq war, and one of them carried a banner declaring "We will wipe Israel from the map".
The Shahab-3 is believed to be derived from technology acquired from North Korea and Pakistan.