Press Secretary Karoline Leavitt confirmed that the Qatari royal family would donate a Boeing 747-8 jumbo jet described as a "flying palace", as Trump prepares to fly out on a Middle East tour that includes Qatar.

"The Qatari government has graciously offered to donate a plane to the Department of Defense. The legal details of that are still being worked out," Leavitt told Fox News.

"But of course, any donation to this government is always done in full compliance with the law, and we commit ourselves to the utmost transparency, and we will continue to do that."

Both the monetary size of the gift and the proposed use of a foreign-built plane as the ultra-sensitive Air Force One would be unprecedented and raise numerous ethical and security questions.

Asked if there were concerns that Qatar would want something in return, Leavitt replied: "Absolutely not, because they know President Trump and they know he only works with the interests of the American public in mind."

The US Constitution prohibits government officials from accepting gifts "from any King, Prince or foreign State," in a section known as the emoluments clause.

But there could be possible loopholes for the jet, including if it is given to the Pentagon, or if Trump later donates it to his planned presidential library after he leaves office.

Trump himself on Sunday defended the plans -- without confirming it was from Qatar -- despite strict rules on presents for US presidents.

"So the fact that the Defense Department is getting a GIFT, FREE OF CHARGE, of a 747 aircraft to replace the 40 year old Air Force One, temporarily, in a very public and transparent transaction, so bothers the Crooked Democrats that they insist we pay, TOP DOLLAR, for the plane," he said on Truth Social.

The US president has long been unhappy with the Air Force One jets -- two highly customized Boeing 747-200B series aircraft that entered service in 1990 under President George H.W. Bush.

Earlier this year Trump said his administration was "looking at alternatives" to Boeing following delays in the delivery of two new 747-8 aircraft.