US President Barack Obama reflected yesterday on eight years in office and expressed optimism for the future of the United States, closing his last remarks to the press by declaring, "At my core, I think we're going to be okay."

In his final press conference before Donald Trump is inaugurated as president tomorrow, Obama defended his recent decision to commute the sentence of convicted whistleblower Chelsea Manning, expressed concern about the fate of the Israeli-Palestinian peace process and spoke forcefully about the role of a free press in a democracy.

Trump has vowed to turn back much of Obama's legacy, seeking to repeal his signature health insurance reforms and suggesting a change of course on issues from immigration to foreign policy.

Obama acknowledged that he expects the Republican president to seek to change much of US policy after an election seen as a rejection of much of the Democrats' agenda.

However he noted, Trump will not know the magnitude of the presidency "until he sits behind that desk" and encouraged him to take the counsel of his advisers.

"This is a job of such magnitude that you can't do it by yourself," Obama said. "You are enormously reliant on a team - your cabinet, your senior White House staff."

Obama, who during the campaign called Trump unfit to hold high office, has largely refrained from directly criticising him since the election and maintained that he wants to hold himself out of politics moving forward.

But he also made clear there were "core values" that he would speak out on if Trump were to cross a line on systematic discrimination, voting rights, silencing the press or deporting immigrants brought to the country as children.

Trump has taken a confrontational line against the press, frequently singling out specific outlets and indicating he might make changes to how the White House interacts with the press.

Obama began his remarks with a strong defence of the press, thanking reporters for holding the administration responsible and casting a critical eye to power.

"My hope is that you will continue with the same tenacity that you showed us, to do the hard work of getting to the bottom of stories and getting them right and to push those of us in power to be the best version of ourselves and to push this country to be the best version of itself," Obama told reporters.

Addressing Russia, which his intelligence agencies said sought to interfere in US elections, Obama urged the United States to continue to stand up for human rights and the principle that large countries do not bully smaller ones, pointing to international sanctions on Moscow over its incursion in Ukraine.

"The United States typically has been on the right side of these issues and it is important for us to continue to be on the right side of these issues," Obama said.

"If we, the largest, strongest country and democracy in the world, are not willing to stand up on behalf of these values, then certainly China, Russia and others will not."

On the Middle East, Obama said a shift in US policy in failing to block a recent UN resolution condemning Israeli settlement activity was designed to send a "wake-up call" that the situation on the ground will increasingly make a two-state solution impossible.

"It's important for the US to send a signal, a wake-up call that this moment may be passing," he said, noting it is unclear how the approach will play out.

Obama leaves office with an approval rating of 57 percent, according to Sunday data from pollster Gallup.

Trump's pre-inauguration approval rating stands at 40 percent - around half of the public support Obama had (78 percent) before his inauguration in 2009, according to the pollster.

President-elect Trump is due to be sworn in tomorrow at noon (1700 GMT), at which point Obama officially leaves office after an eight-year tenure.

Obama would not comment on plans by dozens of his fellow Democrats to boycott the ceremony but noted he and first lady Michelle Obama will be in attendance.

- dpa