Facebook says it has removed and banned hundreds of accounts to disrupt a "violent, anti-government" US network.
It said the network was loosely linked to the broader far-right Boogaloo Bois movement but was distinct because it actively sought to commit violence.
Boogaloo Bois is a loose association advocating overthrow of the government and is committed to gun ownership.
The move comes as Facebook faces a boycott from advertisers over hate speech on the platform.
Major companies including Ford, Adidas, Coca-Cola and Starbucks have pulled advertising from Facebook, urged on by campaigners who say the social media firm doesn't do enough to remove racist and other hateful content.
On Tuesday, Facebook said it was disrupting the "dangerous" network on its platform.
"It is actively promoting violence against civilians, law enforcement and government officials and institutions," a statement said.
"Members of this network seek to recruit others within the broader Boogaloo movement, sharing the same content online and adopting the same offline appearance as others in the movement to do so."
The Boogaloo Bois movement shares followers with some neo-Nazi and white supremacist groups, as well as libertarians and anarchists.
Facebook removed 220 accounts on its namesake platform and another 95 accounts from Instagram, as well as 28 pages and 106 groups that "currently comprise the network".
"We have also removed over 400 additional groups and over 100 other pages for violating our Dangerous Individuals and Organisations policy," it said.
It added that the removal of the accounts was "the latest step in our commitment to ban people who proclaim a violent mission from using our platform".
The social media site said it had been closely following the Boogaloo movement since 2019.
How members have responded
By Shayan Sardarizadeh, BBC Monitoring
Although major Boogaloo Bois pages and groups with tens of thousands of members have vanished overnight, a few smaller ones are still up as Facebook says it will differentiate between the wider online community of Boogaloo supporters and those who identify as members of the Boogaloo Bois group.
A number of groups and pages anticipated the takedown a couple of weeks ago and removed any reference to the term Boogaloo from their names. The move seems to have worked for a few of them, but not all.
The administrators of a number of smaller pages that survived the cull have already told their followers to set up new pages and groups.
Overall, this is clearly a huge hit to those active in Boogaloo Bois groups. Relatively small on 4chan in its early days, it was the movement's presence on Facebook that helped it rapidly expand and attract thousands of new members.
TikTok and Discord have also moved to remove accounts linked to the group from their platforms in recent days.
Members of these groups may well now simply move the conversation to the hundreds of existing firearm-themed pages and groups on Facebook, or try to relocate to smaller, less mainstream platforms such as Parler and Telegram.
The Boogaloo Bois is loose and leaderless. Followers generally sign up to two fundamental beliefs - a desire for an armed overthrow of the government, and an unwavering commitment to gun ownership.
It began as a relatively small movement on 4chan, an imageboard website allowing anonymous posts on controversial topics which has been linked to the rise of the alt-right. However, over the years the Boogaloo Bois has grown considerably in size.
Last month, a US Air Force sergeant with links to the movement was charged with the murder of a federal security officer during a Black Lives Matter protest. He was also charged with the murder of another officer eight days later.
Armed members dressed in Hawaiian shirts and military fatigues have been seen attending Black Lives Matter rallies, claiming they were there to "protect the protesters from police". But analysts say they are increasingly capitalising on the protests to attack the authorities.
US Attorney General William Barr last week formed a Justice Department task force to counter violent anti-government extremists including the Boogaloo movement.