The European Union should maximise the pressure on Iran's economy by imposing an embargo on oil imports from the country by the end of this month, Alain Juppe, the French foreign minister, said yesterday.
This would stop Iran from selling 450,000 barrels to Europe every day, potentially depriving the country of 30pc of its oil exports.
This possible threat to its principal source of revenue has already drawn a belligerent response from Iran, which said it would respond by blocking the Strait of Hormuz, the most important link in the global oil supply chain.
Yesterday, Iran criticised the US for sending an aircraft carrier through the strait and cautioned America not to repeat this move.
"We recommend to the American warship that passed through the Strait of Hormuz and went to Gulf of Oman not to return," said General Ataollah Salehi, commander of Iran's regular armed forces.
Last month, EU foreign ministers failed to agree an oil embargo, largely because of objections from Greece, Italy and Spain, who together buy most of Iran's crude exports to Europe.
However, Mr Juppe signalled a renewed drive to secure a ban.
"Iran is pursuing the development of its nuclear arms, I have no doubt about it," he told French television, adding that France had responded with a unilateral decision not to buy Iranian oil.
"We want the Europeans to take a similar step by January 30 to show our determination."
Any such embargo would amount to "biting sanctions in the real sense of the word", said Mark Fitzpatrick, a director at the International Institute for Strategic Studies.
But Iran's threat to retaliate by closing the Strait of Hormuz was "bluster", he added. "That would invite a military attack and prevent Iran's own oil from going through the strait."
But other observers took a different view. Nigel Kushner, chief executive of Whale Rock, a legal practice specialising in international trade and sanctions, said that Iran's warning should be taken seriously.
"The Iranians would find it difficult not to take quite drastic action if the EU does ban their oil imports," he added.
In a separate development yesterday, French President Nicolas Sarkozy demanded the resignation of Bashar al-Assad after accusing the Syrian leader of perpetrating a massacre against his own people.
Mr Sarkozy's denunciation came as the Arab League stepped up pressure on Mr Assad by hinting its observers in Syria could be withdrawn. (© Daily Telegraph, London)