Facebook has referred its decision to suspend Donald Trump to its independent Oversight Board, opening the possibility that the former president's ban could be overturned.
The social media giant indefinitely blocked Mr Trump's ability to post on both Facebook and Instagram on January 7, after he used the service to praise the Capitol Hill attackers in messages that many saw as encouraging further violence.
Sir Nick Clegg, Facebook's global head of policy, said on Thursday that Trump's ban would remain in place until at least after the board had ruled, which could take up to 90 days. The board has accepted the case.
Often described as Facebook's "supreme court", the board has the power to reverse Facebook's decisions based on user appeals. It is made up of 20 experts including former Guardian editor Alan Rusbridger and former Danish prime minister Helle Thorning-Schmidt.
Trump's ban is likely to be its most high-profile case since its launch in October, and a major test of whether the board can increase public confidence in Facebook's often unaccountable censorship decisions.
Separately, the US House of Representatives has asked the FBI to investigate the role of Parler, an alternative social network popular with Trump supporters and various far Right groups, in this month's violence at the Capitol.
Clegg said: "Our decision to suspend then-President Trump's access was taken in extraordinary circumstances: a US president actively fomenting a violent insurrection designed to thwart the peaceful transition of power; five people killed; legislators fleeing the seat of democracy.
"This has never happened before — and we hope it will never happen again. It was an unprecedented set of events which called for unprecedented action. Our first priority was to assist in the peaceful transfer of power....
"We believe our decision was necessary and right. Given its significance, we think it is important for the board to review it and reach an independent judgment on whether it should be upheld."
Clegg added that Facebook had requested policy guidance from the board on how it should deal with elected leaders who break its rules in future, which he admitted had made many people "uncomfortable".
The Oversight Board said: "Mr Trump's [suspension] has driven intense global interest. The Board is ready to provide a thorough and independent assessment of the company's decision."
The former president's suspension caused uproar around the world, with some breathing relief that he should have been kicked off earlier and others, including US conservatives and European leaders, voicing disquiet at a global tech company having the power to ban an elected head of government.
At the time, Facebook's chief executive Mark Zuckerberg said the company had judged that Trump's posts would have the effect of provoking further violence, and said the risks of letting him stay on the service were "simply too great".
The case will now be examined by a panel of five board members, whose decision will need to be ratified by a vote of the whole board. Trump will have the right to submit a statement, as well interested members of the public.
Zuckerberg first proposed the board in 2018 as a way of checking Facebook's vast global power over online speech, which has only grown since then as the company's services gained an estimated 500m more users.
The company has committed to honouring the board's rulings about content that has been taken down, and to consider and publicly respond to the board's recommendations for future policy.
Many activists and experts have welcomed the board, though some have dismissed it as a sham whose powers are too narrow to truly hold Facebook accountable. Conservatives have also accused it of left-wing bias, pointing to the prominence of liberal figures such as Rusbridger.