Almost seven months into their war, Tehran and Washington remain locked in a stalemate, though neither side appears willing to return to full-scale war, said AFP.
In a statement, a spokesman for the Iranian Revolutionary Guards Corps, the ideological arm of Iran's military, said "there will certainly be significant changes in our defense and our counteroffensive" in the event of a new US attack.
"We will introduce new weapons with new capabilities into the battlefield, and the world will be surprised," he said.
"Our targets will not necessarily be the same as before either. We have new targets that have not yet been attacked."
The Guards also said they were prepared for a "prolonged war".
On Saturday, the central command of Iran's military said the US was planning new action against Tehran, according to state television, but it did not elaborate.
Fighting between the US and Iran has eased in recent days after a flare-up at the end of last month, though Tehran continues sporadic attacks on commercial ships in the Strait of Hormuz.
Both sides are maintaining rival blockades in the waterway in an effort to exert pressure.