Iran has threatened to block the strategic Strait of Hormuz if its interests are seriously threatened, a senior Iranian military commander has said.
A fifth of the world's oil flows through the passageway at the mouth of the Persian Gulf.
General Hasan Firouzabadi told state media: "We do have a plan to close the Strait of Hormuz.
"A Shia nation (Iran) acts reasonably and would not approve interruption of a waterway ... unless our interests are seriously threatened."
The comments by Gen Firouzabadi, the chairman of Iran's Joint Chiefs of Staff, comes days after the European Union enforced a total oil embargo against Iran for its refusal to halt its uranium enrichment programme.
A halt in crude oil imports from Iran is intended to increase pressure on the Islamic Republic to stop enriching uranium to the 20% level, an issue at the centre of an international dispute.
Western powers fear material produced at that level - well above the 3.5% enrichment needed for energy-producing reactors - can be turned into weapons-grade material in a matter of months. Iran insists its reactors are only for energy and research.
Iranian politicians have prepared a Bill that would order the country's military to stop tankers headed to countries that have joined the oil ban.
But Iran's parliament speaker, Ali Larijani, was quoted by Iranian media as saying that the proposed Bill has not yet been studied by parliament.
Iran's powerful Revolutionary Guard has warned in the past that Tehran would order the closure of the Strait of Hormuz if the country's oil exports are blocked.