Donald Trump secretly swapped planes as he left a Nato summit in Turkey last month, as part of an elaborate ruse in response to a possible Iranian threat, US media report.
The US president boarded Air Force One in view of television cameras before being transported to a military aircraft with the help of a catering truck, the Washington Post said. Journalists and some White House staff on board did not know he had been smuggled out.
Officials told the BBC's US partner CBS News that the US had detected a credible Iranian threat to fire a missile at the plane. The White House has not confirmed the secret switch.
Trump had earlier said he was Iran's "number one target" during the summit in Ankara.
The clandestine manoeuvre came a day after the US renewed military strikes on Iran following a breakdown of negotiations between Washington and Tehran to end the war.
Trump had arrived in Turkey aboard a newer Boeing 747-8 donated by Qatar, but announced that he would leave on the old Air Force One "for old time's sake".
On 8 July, footage showed him boarding the presidential jet at Ankara airport. But according to the Washington Post, he was then secretly taken to a smaller C-32A military aircraft - a modified Boeing 757 often used by the vice-president - via a catering truck which had been elevated to plane level on the opposite side to where he had boarded.
Defence Secretary Pete Hegseth boarded the C-32A separately using external stairs in an effort to make the flight appear normal, according to the newspaper.
Journalists and some White House staff boarded Air Force One and were reportedly told to close their window shades. They were unaware the president was no longer on board.
Trump then flew to the UK en route to the US, where he reboarded the old Air Force One and was seen descending from the aircraft after it landed at RAF Mildenhall. It is unclear how he moved from the C-32A back to the legacy jet.
