An Iranian assassination threat against US President Donald Trump prompted an extraordinary operation last month in which he flew secretly from Turkey on an alternate military aircraft while the White House said he was aboard Air Force One, reports The Washington Post.

Contrary to public statements, Trump secretly left Turkey, leaving the NATO summit amid the Iranian threat.

The White House had said the president was on Air Force One when he left the NATO summit. In reality, his departure was carefully planned to conceal his movements.

Trump had arrived in Ankara for the NATO summit on a recently refurbished plane provided by Qatar, but unexpectedly used an older Air Force One to depart the country, raising questions about the safety of the new plane.

Reporters who believed they were traveling with Trump on the old presidential Air Force One, which was actually used as a decoy, said they were advised to keep the curtains closed in the press box.

When reporters later asked Trump why they had to keep the curtains closed during the flight, he said it was because they were probably on a dangerous flight.

The C-32A carrying Trump had departed from the UK and arrived at around 10:20 p.m., while the older Air Force One and the media members aboard arrived a few minutes later.

It is unclear how Trump was transferred from the C-32A back to the older Air Force One.