Donald Trump's national security adviser has been telling a story on Capitol Hill about how the president called him at 3am to ask whether a strong or weak dollar was good for the US economy.

Two sources have told the Huffington Post that Michael Flynn has been recounting the story. He advised the president the health of the US dollar was not his speciality and Trump should ask an economist.

Flynn, a retired lieutenant-general, spent his career in counter-intelligence and was forced into retirement by the Obama administration in 2014. This was because, critics claimed, his management style was chaotic. In a final interview before leaving his post, Flynn said he had been forced out for his views on Islamic terrorism.

After Flynn told Trump that he could not advise him on the dollar, the president was not pleased, said the Huffington Post's sources familiar with Flynn's accounts. The White House has not replied to a request for comment at the time of publication.

In an interview with Fox News pundit Bill O'Reilly aired on Tuesday (7 February), Trump said that in his first weeks as president he had been working "long hours" and frequently only gets about four or five hours of sleep a night. He typically works until midnight or 1 am and wakes up at 5am to eat, read newspapers and watch television news.

Trump confesses that at the start of his presidency he has been surprised by "the size, the magnitude of everything". Being president can be a "surreal experience in a certain way," he said.

National Security Adviser Michael Flynn (right) told Donald Trump the health of the US dollar was not his speciality Reuters/Carlos Barria