Facebook whistleblower Frances Haugen said the social media platform was used to fan the flames of violence in Ethiopia.
In her testimony before a US Senate subcommittee, she said the social media giant could be used dangerously if action is not taken.
In 2019, Facebook was blamed for the spread of violence in Ethiopia after an Oromo activist Jawar Mohammed accused the government of endangering his life, sparking protests.
At the time, Ethiopian running legend Haile Gebrselassie told the BBC that fake news shared on Facebook was behind violence in which 78 people died, warning that “fake news is easy to spread”.
Facebook says it has a policy of “working to fight the spread of false news”.
Ms Haugen gave the example of Myanmar where Facebook admitted to not doing enough to stop the spread of hate posts.
“My fear is that without action, divisive and extremist behaviours we see today are only the beginning,” she said.
The former Facebook employee said the company gives priority to its profits over the safety of users.
The tech giant said it did not agree with Ms Haugen’s “characterization of the many issues she testified about”.