Trump called the decision and his banning across tech platforms "a total disgrace" and said the companies would "pay a political price".

The much-awaited board verdict has been watched for signals on how the world's largest social media company will treat rule-breaking political leaders in the future, a key area of controversy for online platforms.

The board, created by Facebook to rule on a small slice of its content decisions, said the company was right to ban Trump following the January 6 storming of the US Capitol by pro-Trump supporters.

Facebook indefinitely blocked Trump's access to his Facebook and Instagram accounts over concerns of further violent unrest following the January 6 riot.

It enacted the suspension after removing two of Trump's posts during the Capitol riot, including a video in which he said supporters should go home but reiterated his false claim of widespread voter fraud, saying: "I know your pain. I know you're hurt. We had an election that was stolen from us."

But the board said Facebook inappropriately imposed a suspension without clear standards and the company should determine a response consistent with rules applied to other users.

It said the company could determine that Trump's account could be restored, suspended temporarily or permanently banned.

"Indefinite penalties of this sort do not pass the international or American smell test for clarity, consistency, and transparency," said former federal judge and board co-chair Michael McConnell during a news conference on Wednesday.

The board said Facebook's existing policies, such as deciding when material is too newsworthy to remove, needed to be more clearly communicated to users.

It also called on Facebook to develop a policy that governs how it handles novel situations where its existing rules would be insufficient to prevent imminent harm.

Trump called the board's decision "a total disgrace and an embarrassment to our country", and added "free speech has been taken away from the president of the United States because the radical left lunatics are afraid of the truth, but the truth will come out anyway, bigger and stronger than ever before".

Tech platforms have grappled with how to police world leaders and politicians who violate their guidelines.

Facebook has come under fire both from those who think it should abandon its hands-off approach to political speech and those who saw the Trump ban as an act of censorship.

Facbook was one of a slew of social media sites that barred the former president, including Twitter, which banned him permanently.

Trump had a combined 59 million followers across Facebook and Instagram.

On Tuesday, Trump launched a new web page to share messages that readers can re-post on Facebook or Twitter.

Trump also plans to launch his own social media platform.

Australian Associated Press