The US has warned Iran it will not tolerate any disruption of traffic through the Strait of Hormuz after Iran threatened to choke off the vital Persian Gulf oil transport route if Washington imposes sanctions targeting its crude exports.
The increasingly heated exchange raises new tensions in a stand-off that has the potential to spark military reprisals and send oil prices soaring.
Iran's navy chief boasted that it would be "very easy" for his country's forces to close the strategic Strait of Hormuz, the passage at the mouth of the Persian Gulf through which a sixth of the world's oil passes daily.
It was the second such threat in two days following a warning by Iran's vice president that Tehran was close
"Iran has comprehensive control over the strategic waterway," Admiral Habibollah Sayyari told state-run Press TV, as the country was in the midst of a 10-day military drill near the strategic waterway.
The comments drew a quick response from the US
"This is not just an important issue for security and stability in the region, but is an economic lifeline for countries in the Gulf, to include Iran," Pentagon press secretary George Little said.
"Interference with the transit or passage of vessels through the Strait of Hormuz will not be tolerated."
Separately, a Bahrain-based US Navy 5th Fleet spokeswoman said the Navy is "always ready to counter malevolent actions to ensure freedom of navigation".
Iran's threat to seal off the Gulf, surrounded by oil-rich Gulf states, underlines the depth of worry over the prospect that the Obama administration will go ahead with sanctions over its nuclear programme that would severely hit its biggest revenue earner, oil.