Merseyside Police has urged people not to speculate about the identity of the Southport knife attacker.
A 17-year-old boy, born in Cardiff and living in a nearby town, has been arrested on suspicion of murder and attempted murder.
Earlier police said the name of a suspect circulated on social media was incorrect.
Police said the unrest tonight broke out after calls for a protest near a mosque close to where the attack happened.
Assistant Chief Constable Alex Goss: “There has been much speculation and hypothesis around the status of a 17-year-old male who is currently in police custody and some individuals are using this to bring violence and disorder to our streets.
“We have already said that the person arrested was born in the UK and speculation helps nobody at this time.”
