UN rights chief Volker Turk on Saturday urged Twitter's new owner Elon Musk to make respect for human rights central to the social network after he sacked around half the company's employees.
Reports of Musk laying off the platform's entire human rights team were "not, from my perspective, an encouraging start", Turk said in an open letter.
The United Nations High Commissioner for Human Rights said he was writing with "concern and apprehension about our digital public square and Twitter's role in it".
He warned against propagating hate speech and misinformation and highlighted the need to protect user privacy.
Musk, the richest person in the world, took control of the platform a week ago in a contentious deal.
After completing his mammoth $44 billion acquisition, Musk quickly set about dissolving Twitter's board and sacking its chief executive and top managers.
Twitter on Friday fired roughly half of its 7,500-strong workforce.
"Like all companies, Twitter needs to understand the harms associated with its platform and take steps to address them," wrote Turk.
"Respect for our shared human rights should set the guardrails for the platform's use and evolution. In short, I urge you to ensure human rights are central to the management of Twitter under your leadership."
Turk posted the open letter on Twitter, where he has more than 25,000 followers.
Turk, an Austrian longtime UN official who took up his post as the UN rights chief on October 17, spelt out some fundamental human rights principles, urging Musk to put them at the heart of Twitter's management going forward.
Turk urged Twitter to stand up for the rights to privacy and free expression to the fullest extent possible, under relevant laws, and to transparently report on government pressures that would infringe those rights.
But he said free speech "is not a free pass", saying that the viral spread of harmful disinformation, as seen during the Covid-19 pandemic, resulted in real-world harms.
"Twitter has a responsibility to avoid amplifying content that results in harms to people's rights," Turk said.
"There is no place for hatred that incites discrimination, hostility or violence on Twitter.
"Hate speech has spread like wildfire on social media... with horrific, life-threatening consequences."
Twitter should therefore continue to bar such hatred on the platform, while every effort should be made to remove such content promptly, said Turk.
He also said free speech depended on the effective protection of privacy.
"It is vital that Twitter refrain from invasive user tracking and amassing related data and that it resist, to the fullest extent possible under applicable laws, unjustified requests from governments for user data," Turk said.
He said research was essential to understand the impact of social media on societies, and therefore urged Musk to maintain access to Twitter's data through its open application programming interfaces.
Finally, he stressed that Twitter should have content moderation capacity in all languages and contexts, not just in the United States or in English-language content.