Iran says it may close a vital oil-trade route if the West imposes more sanctions over its controversial nuclear programme.
Vice-President Mohammad Reza Rahimi warned that "not a drop of oil will pass through the Strait of Hormuz" if sanctions are widened.
Iran's navy chief Admiral Habibollah Sayari later said closing the strait would be "easy".
The US and its allies believe Iran is trying to develop a nuclear weapon.
Tehran insists its nuclear programme is for peaceful purposes.
Oil and finance
Western nations recently unveiled new sanctions against Tehran following a UN report that said Iran had carried out tests related to "development of a nuclear device".
Further measures being considered to target Iran's oil and financial sectors have brought a furious response from Tehran.
"The enemies will only drop their plots when we put them back in their place," Mr Rahimi was quoted as saying on Tuesday by the official news agency Irna.
Adm Sayari later told Iran's Press TV that closing the Strait of Hormuz would be "really easy" for Iran's armed forces "or as Iranians say, easier than drinking a glass of water".
"But right now, we don't need to shut it as we have the Sea of Oman under control, and we can control the transit," he added.
The Strait of Hormuz links the Gulf - and the oil-producing states of Bahrain, Kuwait, Qatar, Saudi Arabia and the United Arab Emirates (UAE) - to the Indian Ocean. About 40% of the world's tanker-borne oil passes through it.
The US maintains a naval presence in the Gulf, largely to ensure the transport of oil remains open.
Washington played down the Iranian threat.
US State Department deputy spokesman Mark Toner said: "I just think it's another attempt by them to distract attention from the real issue, which is their continued non-compliance with their international nuclear obligations."
Iran's navy has been staging wargames in international waters to the east of the strait.
Adm Sayari said the manoeuvres were designed to show Gulf neighbours the power of Iran's military over the zone.
Washington and Israel have not ruled out military action against Iran's nuclear facilities if sanctions and diplomacy fail.
Iran has vowed to respond by attacking Israeli and US interests in the region.
An embargo on Iranian oil exports has been considered before but dismissed as it could also drive up global oil prices and harm Western economies, particularly in Europe.
It is believed the new measures could cut Tehran off from global energy markets without raising the price of fuel.
The UN has ratified four rounds of sanctions against Iran over its failure to halt uranium enrichment and co-operate with the International Atomic Energy Agency (IAEA).