Twitter has suspended more than 70,000 accounts linked to the far-right movement QAnon.
QAnon is a conspiracy claiming that President Donald Trump is waging a war against Satan-worshipping paedophiles in politics, business and the media.
Supporters were involved in the storming of the US Congress building last week.
Twitter has deleted accounts that “share harmful QAnon-associated content at scale”.
“We’ve been clear that we will take strong enforcement action on behaviour that has the potential to lead to offline harm,” Twitter said in a blog post.
“Given the violent events in Washington, DC, and increased risk of harm, we began permanently suspending thousands of accounts that were primarily dedicated to sharing QAnon content on Friday afternoon.”
Twitter said there were “many instances of a single individual operating numerous accounts".
The accounts were primarily dedicated to the propagation of this conspiracy theory across the service, it added.
President Trump - viewed as a hero by the movement - has stopped short of endorsing the conspiracy theory but has described QAnon activists as "people who love our country".
In July last year, Twitter said it would crack down on QAnon accounts on the platform, stop recommending associated content and block URLs linked to it from being shared on the platform.
In 2019, the FBI issued a warning about "conspiracy theory-driven domestic extremists" and designated QAnon a potential domestic extremist threat.
Analysis by Shayan Sardarizadeh, BBC Monitoring
Twitter was one of the first major social networks to impose restrictions on QAnon-linked accounts and content back in the summer of 2020.
But after Facebook and YouTube took sweeping action against the conspiracy in October, Twitter became the only mainstream platform still available to QAnon promoters.
BBC research shows QAnon-related phrases and hashtags were used more than 20 million times on Twitter between January and September 2020.
In the lead-up to the Capitol riots, major QAnon influencers repeatedly called on their followers to attend the rally in Washington DC and made violent statements about Vice-President Mike Pence and other senior members of Congress who refused to overturn the outcome of the election.
While thousands of QAnon-related accounts are still active on the platform, the vast majority of the conspiracy's main influencers with millions of followers in total have now been removed.
With the door closing on all the major platforms and the self-styled "free speech" social network Parler going offline, Gab - another platform popular with right-wing users - is emerging as the go-to place for QAnon followers.
Groups which promote QAnon on Gab have added tens of thousands of followers in the last few days, and now boast more than 400,000 followers in total.