Donald Trump waves at the top of the US Air Force One (Picture: US Air Force).
The US Air Force has ordered a review of all international layovers.
"Air Force leadership directed Air Mobility Command to review all guidance pertaining to selection of airports and lodging accommodations during international travels," the Air Force said in a statement Sunday evening.
The decision follows recent visits by Air Force crew members at President Trump's resort in Turnberry, Scotland, during refuelling stops.
A US Air Force C-17 crew spent time at the Turnberry resort during a refuelling stop to Kuwait in March.
The Air Force had previously launched a separate inquiry into the stays of aircrew members who were directed to land at Prestwick Airport, in Glasgow, Scotland, earlier in the year. The same crew members would then stay at the President's resort in Turnberry.
US Government watchdogs have therefore argued that the arrangements breach ethical norms and could potentially violate a clause of the Constitution of the United States.
The statement by the Air Force said that initial reviews indicate that "aircrew transiting through Scotland adhered to all guidance and procedures".
However, the statement also said that service members lodging at higher-end accommodations "might be allowable but not advisable".
After news of the congressional probe became public, the Air Force has said the stopover of a US Air Force C-17 in Glasgow is "not unusual".
In the case of the flight on 13 March, seven active duty and National Guard crew members stayed at Turnberry.
There are reports that the Air Force stated that the resort in Turnberry was less expensive than a nearby Marriott chain hotel.