British Prime Minister Keir Starmer warned social media companies that they must uphold laws that prohibit the incitement of violence online after misinformation around a fatal mass stabbing earlier in the week sparked violent scenes.A 17-year-old boy appeared in an English court on Thursday charged with the murder of three young girls in a knife attack at a summer dance class in Southport that has shocked the nation and sparked two nights of violent protests. The disturbances followed the rapid spread of false information on social media that the suspect in the stabbings was a radical Islamist migrant, with anti-immigrant protesters descending on Southport from elsewhere, attacking police and targeting a mosque.Starmer said that the disturbances were not legitimate protests, saying it was criminal disorder that was “clearly driven by far-right hatred” before adding a warning to tech companies.“Let me also say to large social media companies, and those who run them, violent disorder clearly whipped up online: that is also a crime. It’s happening on your premises, and the law must be upheld everywhere,” he said at a news conference, adding there was a “balance to be struck” in handling such platforms. “It’s an amazing opportunity that we all enjoy... There is also a responsibility that goes with it. That’s a space for a mature conversation to take place.”Campaign group Hope Not Hate said that the riot in Southport on Tuesday followed a “blizzard of false information around the attack, much of it circulated by far-right accounts online.” The 17-year-old suspect was not initially named due to rules regarding children who are charged with crimes, before a judge then ruled that media could name him as Axel Rudakubana. He turns 18 next week and police have said he was born in Cardiff.But a claim that the suspect was an asylum seeker or immigrant has been viewed at least 15.7mn times across X, Facebook, Instagram and other platforms, a Reuters analysis showed.A false claim that he was an undocumented migrant who arrived in a small boat appeared on the website “Channel 3 Now”, who later apologised for publishing information that was misleading and not accurate.