US President Donald Trump shows a letter from former President Barack Obama at a swearing-in ceremony for senior staff at the White House Reuters/Carlos Barria

President Donald Trump showed off a letter from former President Barack Obama on Sunday (22 January) during a swearing-in ceremony for senior staff in his administration.

"I walked into the Oval Office and found this beautiful letter from President Obama," Trump said, adding that he would not disclose its contents. "It was really very nice of him to do that, and we will cherish that. And we won't even tell the press what's in that letter," he added.

Obama "on his part was wonderful to write it", said Trump, appearing touched by the letter's contents.

It is a tradition for presidents to leave a note offering advice to their successor. These letters eventually become public.

On the day of Trump's inauguration, the US National Archives released a copy of the handwritten note that George W Bush left for President Barack Obama on 20 January 2009.

"There will be trying moments. The critics will rage. Your 'friends' will disappoint you," Bush wrote to Obama, noting that few people know the responsibility presidents feel. But "no matter what comes," Bush continued, "you will be inspired by the character and compassion of the people you now lead."