Iran has threatened to close the vital Strait of Hormuz to the United States and its allies if they threaten the regime in Tehran.
The Strait of Hormuz is a key pinchpoint at the eastern end of the Persian Gulf and a third of all oil traded by sea is said to pass through it.
Last summer Iran agreed a deal with the US and five other world powers to scale down its controversial nuclear programme in return for the lifting of crushing economic sanctions.
But the rapprochement with Washington seems to be in danger already with the belligerent remarks of a key Revolutionary Guard commander.
General Hossein Salami, the deputy commander of Iran’s Revolutionary Guard, said: ‘Americans should learn from recent historical truths.’
He is believed to have been referring to the humiliating capture in January this year of 10 US Navy sailors who accidentally entered Iranian waters.
The sailors were released within 24 hours but only after Iranian state TV aired footage of them on their knees with their hands on their heads.
Gen Salami said: ‘If the Americans and their regional allies want to pass through the Strait of Hormuz and threaten us, we will not allow any entry.
‘Americans cannot make safe any part of the world.’
His remarks follow comments made by Iran’s Supreme Leader Ayatollah Ali Khamenei on Monday.
Ayatollah Khamenei criticised US activities in the Persian Gulf.
Kuwait, Bahrain, Qatar, Saudi Arabia, Iraq and the United Arab Emirates all rely on the Strait of Hormuz to export oil by tanker to Europe and the Far East.
Lieutenant Rick Chernitzer, a spokesman for the US Navy’s 5th Fleet in Bahrain, said: ‘We continue to operate in accordance with professional maritime standards and international law’ in the region.
He said: ‘We remain thoughtful, vigilant and responsible mariners as we conduct our operations here. We do, however, reserve the inherent right to self-defence.’
The two countries have clashed heads before in the Gulf.
In April 1988 they fought a one-day naval battle after the frigate USS Samuel B Roberts was almost sunk by an Iranian mine during the Iran-Iraq war.
US forces attacked two Iranian oil rigs and damaged six Iranian vessels.
Three later the USS Vincennes shot down an Iranian airliner heading to Dubai, killing all 290 civilians on board, after mistaking it for an Iranian fighter jet.
Earlier this year the Iranians began buzzing US vessels with military drones and in December last year the Iranians carried out what Washington described as a ‘highly provocative’ rocket test.
Iran’s state-run IRNA news agency quoted Iran’s Foreign Ministry as saying the country will take any necessary action to maintain security, peace and stability of the region.
US Congressman Randy Forbes was even criticised this week by Iran over a resolution in Congress which referred to the Arabian Gulf, rather than the Persian Gulf.