The comments "are a reiteration of previous assertions that it will not embark on the production of the Shahab-4 missile," said State Department spokesman Richard Boucher.
"It remains unclear what tangible effect this will have on Iranian missile development," he said.
"We've repeatedly expressed our concerns about Iranian behavior, including its development of weapons of mass destruction and missile capabilities," Boucher added.
"But we'll just have to see whether it becomes a positive development or not, in terms of what the Iranians actually do."
Tehran said in a statement Wednesday, "As we have said on several occasions and contrary to certain statements, Iran has no programme to build a Shahab-4 missile."
During a major military parade on September 22, Iran showed off six of its Shahab-3 missiles, which recently went into service with a touted range of more than 1,500 kilometers (932 miles).
According to a commentary given over loud-speakers lining the parade route, the missiles -- decorated with anti-Israeli and anti-US slogans -- have "a range of 1,700 kilometers" (1,060 miles) and "are capable of hitting the heart of the enemy".
The development of the missiles has sparked widespread concern in Israel.