Twitter has suspended at least three accounts tied to far-right group Britain First, including one that had been retweeted by President Trump.
Asked why the accounts had been suspended, Twitter said it would not comment on individual accounts for privacy and security reasons.
But the social media firm did publish a blog post on Monday saying that it would start enforcing rule updates that are designed to reduce "hateful and abusive" content.
The policies prohibit accounts that "affiliate with organizations that use or promote violence against civilians to further their causes." They also ban content that "glorifies violence or the perpetrators of a violent act."
Representatives from Britain First could not immediately be reached for comment.
In its mission statement, Britain First describes itself as "a patriotic resistance and 'frontline' for our long suffering people" that will "restore Christianity as the bedrock" of national life and put British workers first.
But it is far from being a mainstream organization in the U.K.
It has no elected representatives at any level of British politics and has been "deregistered" as a political party by the U.K. Electoral Commission. Its occasional protests rarely attract crowds of more than a few dozen.
Fransen was found guilty of religiously aggravated harassment in November 2016 after verbally abusing a Muslim woman wearing a hijab while she was with her four children. She was fined by the court and ordered to pay costs.
The videos retweeted by Trump's account allegedly depict Muslims assaulting people and, in one video, smashing a statue of the Virgin Mary.
One of the videos purports to show a young "Muslim migrant" attacking a boy on crutches. The Dutch attorney general's office, which handled the case, said the incident occurred in May and the suspect was born and raised in the Netherlands. A spokesperson would not comment on the suspect's religion, saying it was against their policy to share such information.
White House press secretary Sarah Sanders defended Trump's retweets at the time, telling reporters that he shared them to start a conversation about border security and immigration.
But the retweets were met with immediate outrage in the U.K. and resulted in a rare rebuke from the British government toward its American ally.
A spokesperson for Prime Minister Theresa May said Trump was "wrong" to share the videos, adding that "Britain First seeks to divide communities through their use of hateful narratives which peddle lies and stoke tensions."
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