Ethical questions are raised over a US Secret Service ruse that used a plane full of journalists as a possible "decoy" in response to an alleged Iranian threat to shoot Air Force One out of the sky.

Donald Trump let the press pool and some of his staff think he was on Air Force One, while really he had been smuggled in a catering cart onto a different plane.

The president was quietly whisked away and flown on board the smaller Boeing C-32A instead of the larger jet that usually serves as Air Force One.