Donald Trump has separated himself from his family's real estate and golf business.

President Donald Trump on Monday denied anything improper in the use by military personnel and Vice President Mike Pence of his luxury golf resorts while on official travel abroad.

The Air Force announced a review following an uproar over the revelation that the crew of a C-17 transport plane stayed at the Trump Turnberry in Scotland during a layover between Kuwait and Alaska.

Similar questions have been raised over the ethics of Pence and his entourage staying at the Trump family's Doonbeg golf resort in Ireland this month while on an official visit to the country.

Trump, who has raised eyebrows by integrating his family business empire's golf courses into his own presidential schedule, said that government officials' use of his properties was a coincidence.

"NOTHING TO DO WITH ME," he tweeted about the Air Force use of Turnberry, although he added that the officers "have good taste!"

He also defended the Pence group's use of Doonbeg, saying the vice president wanted to visit the town because of family links, even though his official meetings were in Dublin, on the other side of Ireland.

"I had nothing to do with the decision of our great @VP Mike Pence to stay overnight at one of the Trump owned resorts in Doonbeg, Ireland. Mike's family has lived in Doonbeg for many years, and he thought that during his very busy European visit, he would stop and see his family!"

The Pentagon said in a statement that the Scottish layover "adhered to all guidance and procedures," but it acknowledged that there might be at least an image problem.

"We understand that US Service members lodging at higher-end accommodations, even if within government rates, might be allowable but not advisable," the military said.

"We must still be considerate of perceptions of not being good stewards of taxpayer funds that might be created through the appearance of aircrew staying at such locations," it said.

"Therefore, we are reviewing all associated guidance."

Democrats, who control the House of Representatives, said last Friday that they will probe whether Trump has broken laws against profiting from the presidency.

Trump has separated himself from his family's real estate and golf business. However, he makes regular use of his own golf courses in Florida, New Jersey and Virginia.

While at the G7 summit in France, he pitched his Doral resort in Florida as the venue for next year's gathering, arguing that his property is almost unique in the United States as a suitable location for the huge event.