WASHINGTON : US President Donald Trump secretly flew out of Turkey last month on a smaller plane than previously known due to an assassination threat from Iran, the Washington Post reported Monday.

According to an anonymous US official who spoke to the Post, Trump boarded an Air Force One jet in Ankara on July 8, but then moved into a catering container attached to the plane.

The container then ferried him to a smaller C-32A aircraft that flew him to Britain, while media and some officials were led to believe Trump was still on the bigger jet.

The Iranian threat had previously been reported by US media as the reason that Trump did not fly out of Turkey aboard the new Boeing 747-8, gifted to the United States by Qatar, which he had used to fly into the country.

Trump, who was in Ankara for a NATO summit, said at the time he would be taking the older Boeing 747 so that members of the US military at an airbase in Britain could tour the new plane.

However, several US media outlets, including the New York Times, reported that a threat from Iranian proxy forces had prompted the switch.

Journalists on the old plane out of Ankara were also told to keep their window blinds down -- a step normally reserved for war zones -- furthering suspicions of security concerns.

The plane swap prompted renewed scrutiny of the Qatar-gifted jet, which the Times reported did not have the same security features as the older jet, including anti-missile defenses.

Qatar's royal family donated the luxury airliner last year after Trump complained about the state of the two aging Boeing 747 jets that had served as Air Force One since 1990.

The plane was then rapidly retrofitted and flew Trump for the first time on July 1, to North Dakota.

Just days later, he took it on its first overseas trip to Turkey.

When queried by AFP about the Washington Post report, the White House sent a statement defending the new plane's safety.

"The new Air Force One is a state-of-the-art aircraft that has been fitted with high-level security protocols that ensure the safety of the President and his staff," Communications Director Steven Cheung said in the statement.

"As the President has said recently, there are many enemies of America who have their sights on him, and we use every tool at our disposal to address those threats."

The same statement had been used by the White House last month when questions about the aircraft's safety first surfaced.

Video in the Washington Post's report shows a catering truck lowering from the older Air Force One jet, minutes after Trump walked up stairs into the plane.

The catering vehicle can then be seen transiting in the distance to the smaller C-32A aircraft.

After both planes landed in the United Kingdom, Trump was videotaped coming down the steps from the larger jet, before making his way to the new retrofitted Air Force One.

It was unclear how he had made the transfer back to the larger plane, the Post said.