You're talking about Vietnam and at that time nobody had ever heard of the country: Donald Trump

US President Donald Trump on Wednesday said he has no regrets about being able to avoid serving during the Vietnam war, because he was not a "fan" of the highly unpopular conflict.

"I was never a fan of that war, I'll be honest with you. I thought it was a terrible war. I thought it was very far away," Trump told interviewer Piers Morgan on ITV television while visiting Britain for ceremonies marking the 75th anniversary of the D-Day invasion in World War II.

"You're talking about Vietnam and at that time nobody had ever heard of the country," Trump said. "This isn't like 'I'm fighting against Nazi Germany, we're fighting against Hitler.'"

Trump graduated from the Wharton School of Finance in 1968, becoming eligible for the draft to be sent to the war which, despite his comment, was at a peak in that year, with around half a million US soldiers deployed.

It was also the year of the Tet offensive, a failed push by communist forces into US-backed South Vietnam that left thousands dead and marked a turning point - electrifying the US anti-war movement and eventually prompting the Americans to withdraw.

Shortly after Trump left Wharton, a doctor diagnosed bone spurs in his heels, a condition enabling him to get a medical deferment from the draft.

He had already received four previous deferments because he was studying.

Trump, who at the time was a keen sportsman and had attended a military school before going to college, has offered a variety of explanations over the years for how and why he did not serve in Vietnam, instead going on to pursue a career in real estate.

His avoidance of combat was hardly unusual among young Americans from wealthy families or those able to go to college.

These include former presidents George W. Bush who served in the Air National Guard and was never sent abroad, and Bill Clinton, who received education deferments and has been accused of maneuvering to avoid the draft.

Democratic 2020 presidential candidate Joe Biden also received five student draft deferments during the war and was later given a medical exemption due to previous asthma as a teenager.

Trump told Morgan that he would "have been honored" to be called up for a war that he supported and said that his administration's extra funding of the Pentagon compensates for his lack of military service.

"I think I make up for it right now," he said.

More than 58,000 Americans were killed in Vietnam, a fraction of the many more Vietnamese estimated to have died in the conflict.