WASHINGTON • In a letter left on Inauguration Day for US President Donald Trump that was congratulatory and cautionary, departing president Barack Obama urged the incoming leader to guard democratic institutions and traditions, and "sustain the international order".

"This is a unique office, without a clear blueprint for success, so I don't know that any advice from me will be particularly helpful," Mr Obama wrote in the letter, which CNN published on Sunday.

CNN reported that the letter was written in longhand on White House stationery and left in the top drawer of the Resolute Desk in the Oval Office. The letter highlighted the concerns of a departing president who acknowledged the enormous responsibility of the job, domestically and on the world stage.

Mr Obama wrote to Mr Trump, a billionaire who had family wealth and made fortunes in real estate, that "we've both been blessed, in different ways, with great good fortune," adding that "not everyone is so lucky."

It is important to "build more ladders of success for every child and family that's willing to work hard", Mr Obama wrote.

He also emphasised that "our wealth and safety" depend on maintaining "the international order that's expanded steadily since the end of the Cold War".

And he made a case for preserving "instruments of democracy" regardless of what the "push and pull of daily politics" may bring.

It is a tradition for presidents leaving office to write letters to their successors offering advice and well wishes.

Mr Trump has spent much of his presidency trying to undo the policies and regulations of the Obama administration. Even so, Mr Trump has spoken warmly of the letter, telling ABC News in January that it was "beautiful" and "complex".

NYTIMES