Facebook says it will restrict the right-wing conspiracy movement QAnon and will no longer recommend that users join groups supporting it, although the company is not banning it outright.
The social media giant is banning groups and accounts associated with QAnon and a variety of US-based militia and anarchist groups that support violence.
However, the company will continue allow people to post material that supports these groups as long as they do not otherwise violate policies against hate speech, abuse and other provocations.
QAnon groups have flourished on Facebook in recent years. Twitter announced a similar crackdown recently.
The QAnon conspiracy theory is centred on the baseless belief that President Donald Trump is waging a secret campaign against enemies in the “deep state” and a child sex trafficking ring run by satanic pedophiles and cannibals.
For more than two years, followers have pored over tangled clues purportedly posted online by a high-ranking government official known only as “Q”.
The conspiracy theory emerged in a dark corner of the internet but has recently crept into mainstream politics. Trump has retweeted QAnon-promoting accounts and its followers flock to his rallies.
Last week, Marjorie Tyler Greene, a House candidate who openly supports QAnon, won her Republican primary in Georgia. She is part of a growing list of candidates who have expressed support for QAnon.
Facebook says it will only remove groups and accounts outright if they discuss potential violence, including in veiled language.
It has removed more than 790 groups, 100 pages and 1500 ads tied to QAnon, and has blocked more than 300 hashtags across Facebook and Instagram.
There are 1950 other groups and 440 Facebook says it has identified that remain on the platform but face restrictions, along with 10,000 accounts on Instagram.
For militia organisations and those encouraging riots, the company has removed more than 980 groups, 520 Pages and 160 ads from Facebook.