Around one-third of the world's oil passes through a narrow channel between Iran and Oman - the Strait of Hormuz. The Iranian government has been looking increasingly isolated as Syria - where it maintains influence - slides towards civil war, and as international pressure rises over the regime's attempts to develop nuclear weapons. Earlier in December, an Iranian politician, Parviz Sarvari, warned that the country would shut off the strait as part of a military exercise. The country has previously threatened to use its strategic position in the energy market as a weapon. Oil prices rose on December's threat, but bigger concerns over the world economy meant that markets' attention were focused elsewhere. But with a real possibility of Israeli airstrikes, should Iran appear close to getting somewhere with its nuclear programme, comes an appreciable threat of retribution and the closure of a key supply route for oil and liquefied natural gas.