There was a “clear connection” between the violent disorder in England and Northern Ireland in the summer and posts on social media and messaging apps, Ofcom has concluded.
The government had asked the media regulator to consider how illegal content and disinformation spread during the unrest.
In an open letter setting out its findings, external, Ofcom boss Dame Melanie Dawes said such content spread “widely and quickly” online following the stabbings in Southport, in July, which preceded the disorder.
She added most online services took “rapid action”, but said the responses of some firms were “uneven”.
“Misinformation appeared online almost immediately after the attacks, some of it appearing to have malicious intent and seeking to influence public opinion and reaction,” Dame Melanie wrote.
“Posts about the Southport incident and subsequent events from high-profile accounts reached millions of users, demonstrating the role that virality and algorithmic recommendations can play in driving divisive narratives in a crisis period,” she added.