So what's behind this, how would it work and what are the risks? Kharg Island has long been Iran's chief outlet for its oil exports. The island sits offshore with waters deep enough to load product onto tankers known as Very Large Crude Carriers (VLCCs), which can hold around two million barrels. Around 90% of Iran's oil exports pass through Kharg. During the Iran-Iraq war in the 1980s it was frequently bombed by the Iraqi Air Force and on 13 March this year the US struck what it said were 90 military targets on the island. It however spared the oil infrastructure. If the US does decide to invade Kharg Island then it would most likely be a temporary measure intended to put pressure on Iran by cutting off its fuel exports until it relinquished its chokehold on the Strait of Hormuz - one of the world's busiest oil shipping lanes - and conceded to Washington's demands. Given the resilience and defiance of the Iranian regime it is highly questionable whether this would work. The speaker of Iran's parliament, Mohammad Bagher Ghalibaf, has warned that his country's forces would "rain down fire" on any invading US forces. Iran is believed to have reinforced its defences on the island, including with surface-to-air missile batteries. (BBC)