The Obama administration has brushed aside Iran's warning to keep US aircraft carriers out of the Gulf.
The US dismissed its threats as a consequence of hard-hitting American sanctions on the Iranian economy.
Provoking a hostile start to what could prove a pivotal year for Iran, the country's army chief said American vessels were unwelcome in the Gulf, the strategic waterway that carries to market much of the oil pumped in the Middle East.
The Islamic republic has also warned of blocking one of the world's key tanker lanes, the Strait of Hormuz, in response to new, stronger US economic penalties on Iran over its disputed nuclear enrichment programme.
Iranian general Ataollah Salehi's warning about the Gulf came just three days after US President Barack Obama signed into law new sanctions targeting Iran's Central Bank and its ability to sell petroleum abroad.
The US said it was just Iranian sabre-rattling, with no effect on US plans or military movements.
"It's the latest round of Iranian threats and is confirmation that Tehran is under increasing pressure for its continued failure to live up to its international obligations," White House press secretary Jay Carney said.
"Iran is isolated and is seeking to divert attention from its behaviour and domestic problems," Mr Carney added.
The US Navy's 5th Fleet said the aircraft carrier USS John C Stennis and another vessel headed out from the Gulf and through the Strait of Hormuz last week after a visit to Dubai's Jebel Ali port.
Iran closed 10 days of naval manoeuvres on Tuesday, continuing a tone of military defiance but seeing the weight of international sanctions pull its currency, the rial, down to lows against the dollar.