President Donald Trump threatened to seize Iran’s main oil export hub, Kharg Island, on Thursday, before flip-flopping on the grounds that the American people "don't have the stomach" for what military experts say would be an invasion entailing large US casualties.

"The United States will be hitting Iran... VERY HARD TONIGHT," Trump wrote on his Truth Social network on Thursday.

"At some point in the not too distant future, we will be taking Kharg Island, and other oil infrastructure points, and assume total control of their Oil and Gas Markets, much like we have with Venezuela," he added.

The Trump administration considered launching an operation to take Kharg Island in the first month of the war on Iran, but eventually backed off the plan.

Former senior US and western military officials told Middle East Eye at the time that the US would likely be able to establish a bridgehead on Kharg Island, but that a US invading force would face intense fire from Iran as it approached the island and more difficulties trying to hold it.