US President Donald Trump has given Iran a 48-hour deadline, vowing to "obliterate" Iran's power plants if the Strait of Hormuz is not reopened.

Iran has targeted oil, gas and other freight ships in the vital shipping channel - sending energy prices soaring around the world.

The federal government yesterday announced that six fuel tankers scheduled to deliver oil to Australia next month have now been cancelled or deferred with Energy Minister Chris Bowen warning of, "bumps" in future supply.

• GUEST: David Leaney is an expert in international supply chain management and a lecturer at the Australian National University.