Iran on Tuesday threatened to close the Strait of Hormuz, a chokepoint for a third of the world’s seaborne oil trade, if the west imposes oil sanctions on Tehran, causing a rise in oil prices.

The warning by Mohammad Reza Rahimi, Iran’s first vice-president, came days after Iran staged naval war exercises in the strait.

“If they [the West] impose sanctions on Iran’s oil exports, then not even one drop of oil can flow through the Strait of Hormuz,” he told the official Iranian news agency Irna. Iranian officials have in the past threatened to shut down oil traffic through the strait, but the comments by Mr Rahimi are the strongest yet.

France, Germany and the UK are pushing for anembargo on Iranian oil exports to Europe, although several countries, including Greece, have some reservations. EU foreign ministers are scheduled to consider the embargo on January 30.

It was not immediately clear whether Mr Rahimi had official backing for his comments. Only senior commanders of Iran’s Revolutionary Guards can take actions such as closing the strait in the face of foreign threats. Cabinet members such as Mr Rahimi can only try to influence their decision.

The government of Mahmoud Ahmadi-Nejad is engaged in a tense power struggle against conservatives in the Revolutionary Guards, the judiciary and the parliament in advance of parliamentary elections in March, and Mr Rahimi’s remarks could be an attempt by the president’s circle to project an image of strength vis a vis the west and deflect attention from Iran’s economic woes.

The Strait of Hormuz is “the world’s most important oil chokepoint”, according to the US Department of Energy. On average, at least 13-15 supertankers cross the strait every day, most of them heading towards Japan, South Korea, India and China. The US Navy patrols the waterway and analysts believe that Iran would not be able to shut down it.

In late afternoon trading in London, ICE February Brent, the global benchmark, rose $1.21 to $109.17 a barrel. In New York, Nymex February West Texas Intermediate rose $1.47 to $101.15 a barrel. The price surge was amplified by thin trading due to the Christmas holiday. Trading volumes were about a quarter of normal levels.

The price increase was capped by economic weakness in Europe and mild temperatures during the seasonal peak consumption period of the northern hemisphere winter.

But the oil market found additional support on ongoing turmoil in the Middle East and north Africa after Syria confirmed for the first time publicly that it had cut oil production sharply due to the impact of a European Union oil embargo.

Sufian Alao, the Syrian oil minister, revealed over the weekend that Damascus had cut oil production to 260,000 barrels a day, down from a pre-crisis level of 380,000 b/d.

“We have reduced our production by 30 to 35 per cent until we resume exports,” he told reporters on the sidelines of an Arab oil ministers meeting in Cairo on Saturday.

The Syrian oil disruption is relatively small, but oil traders are worried about the potential for a much larger outage involving Iraq after a wave of terror attacks in Baghdad threatened the country’s precarious social balance. “The strong uptick in sectarian violence across Iraq is a serious cause for concern, as it could set back Iraqi production targets by years,” said JBC Energy, the Vienna-based oil consultancy.

On paper, Iraq is set to be a bright spot of oil supply growth in 2012 in an otherwise gloomy market haunted by production disruptions. Baghdad aims to lift oil output to about 3.5m b/d by late next year, up from about 2.8m b/d last month, with the opening of a new export terminal offshore in the Gulf, near its border with Kuwait.