Facebook is testing a feature in the US that asks users if they are worried somebody they know is becoming an extremist.
Other users may also receive an alert saying they may have been exposed to extremist content.
The trial messages are part of Facebook’s Redirect Initiative which aims to combat extremism.
The pop-ups redirect users to a support page.
“This test is part of our larger work to assess ways to provide resources and support to people on Facebook who may have engaged with or were exposed to extremist content or may know someone who is at risk,” a Facebook spokeswoman said.
The tech firm is working with non-governmental organisations and academic experts on this project, she added.
Becoming an extremist?
Screenshots of the pop-ups were posted on social media.
One asked: “Are you concerned that someone you know is becoming an extremist?”
“You may have been exposed to harmful extremist content recently,” another said. “Violent groups try to manipulate your anger and disappointment.
“You can take action now to protect yourself and others.”
Both prompts direct users to a page with support related to extremism.
Facebook said tests identified both users who may have been exposed to rule-breaking extremist content, and users who had previously been the subject of enforcement on the platform.
The company told Reuters it does remove some content and accounts which violate its rules pro-actively before the material is seen by users, but that other content may be viewed before it is taken down.
"We’re seeing an evolving variety of techniques by social media companies to address the seemingly growing problems of mis and disinformation on their platforms," said Jess McBeath, online safety consultant at the UK Safer Internet Centre.
"What’s interesting about this approach is that it taps into the idea that we don’t believe we are influenced by what we see online, but other people are," she added, questioning whether this was how users behaved on the platform.