Two teenage boys died in a road crash before a riot broke out in the Welsh capital of Cardiff that left several police officers injured on Monday night.
South Wales Police dismissed social media rumors that police were involved in the crash, saying officers arrived at the scene after the accident.
"Police responded to this collision which had already occurred when officers arrived, and they remained on scene to manage a large-scale disorder until the early hours of this morning," police said on Tuesday.
Cars were set alight and fireworks thrown at police during the riot, which involved more than 100 people.
It remains unclear how the incident occurred, but initial reports suggested the boys were on an off-road bike or scooter.
"The level of violence towards emergency services and the damage to property and vehicles was totally unacceptable," said Assistant Chief Constable Mark Travis. "Our focus now is to fully investigate the circumstances of the collision and the appalling scenes that followed."
Police said up to 12 officers were injured in the disorder.
"Arrests have already been made in connection with the disorder and more will follow. We shall be maintaining an enhanced police presence throughout the week and into the weekend," Travis said.
A member of the public was also attacked because some of those gathered thought they were an undercover police officer, according to one of the senior officers at the scene.
