Iran says it may close a vital oil-trade route if the West imposes more sanctions over its nuclear programme.
Vice-President Mohammad Reza Rahimi warned that "not a drop of oil will pass through the Strait of Hormuz" if the sanctions are widened.
The Strait of Hormuz links the Gulf to the Indian Ocean. The BBC reports about 40% of the world's tanker-borne oil passes through it.
Iran's navy has been staging wargames in international waters to the east of the strait.
Admiral Habibollah Sayari later said closing the strait would be "easy".
The United Nations has ratified four rounds of sanctions against Iran over its failure to halt uranium enrichment and co-operate with the International Atomic Energy Agency.