A senior Iranian Revolutionary Guards commander said on Thursday that the United States was not in a position to tell Tehran "what to do in the Strait of Hormuz", state television reported.
Tehran's threat to block crude shipments through the crucial passage for Middle Eastern suppliers followed the European Union's decision to tighten sanctions on Iran over its nuclear programme, as well as accompanying moves by the United States to tighten unilateral sanctions.
Iran's English-language Press TV quoted Hossein Salami as saying: "Any threat will be responded by threat ... We will not relinquish our strategic moves if Iran's vital interests are undermined by any means."
Separately, Salami was quoted as saying by the official IRNA news agency: "Americans are not in a position whether to allow Iran to close off the Strait of Hormuz."
The U.S. Fifth Fleet said on Wednesday it would not allow any disruption of traffic in the Strait of Hormuz, a strip of water separating Oman and Iran.
At loggerheads with the West over its nuclear programme, Iran said earlier it would stop the flow of oil through the strait in the Gulf if sanctions were imposed on its crude exports.
Analysts say that Iran could potentially cause havoc in the Strait of Hormuz which connects the biggest Gulf oil producers, including Saudi Arabia, with the Gulf of Oman and the Arabian Sea. At its narrowest point, it is 21 miles (34 km) across.
But its navy would be no match for the firepower of the Fifth Fleet which consists of 20-plus ships supported by combat aircraft, with 15,000 people afloat and another 1,000 ashore.