US President Donald Trump said on Monday that he underwent an MRI (magnetic resonance imaging) scan during his most recent visit to Walter Reed National Military Medical Centre but he declined to provide details about the reason for the scan.

The comments marked the first time Trump, 79, has offered an explanation for his second medical exam this year.

The October 10 visit, described by the White House as a routine yearly check-up, prompted questions about the president’s health as it came just six months after he had an extensive physical examination.

But Trump, who is one of the oldest presidents in US history, would not say why he received the scan, telling reporters travelling with him to “ask the doctors”.

The White House did not immediately respond to questions seeking more detail on the reason for the MRI.

The president said his doctors had offered reporters a “very conclusive” report of the exam, but the White House has not disclosed why Trump made a second visit to Walter Reed, a departure from the traditional presidential cadence of a single comprehensive exam per year.