Cars were set on fire and dozens of young people clashed with police in Wales in what authorities described as "large scale disorder" following a road accident.
The unrest broke out in the district of Ely in Cardiff on Monday night after two teenagers died in a motorcycle crash.
"First and foremost our thoughts are with families of the two boys who have died following the collision in Ely and with those affected by the disorder which followed," said South Wales Police Assistant Chief Constable Mark Travis.
"These are scenes we do not expect to see in our communities, particularly a close-knit community such as Ely."
Footage posted to social media showed dozens of young people, many wearing ski masks or hoods, throwing rocks and launching fireworks toward police officers who were blocking the end of the street with riot shields.
Officers on horseback were stationed outside the Ely police station early on Tuesday after suggestions that it could be targeted.
Police made arrests but did not specify how many. A dozen officers were injured in the unrest, police added.
Rumors of a police chase
The unrest reportedly began after residents suspected a police chase was the cause of the fatal accident.
However, South Wales Police said the crash "had already occurred when officers arrived."
"My understanding is that there was a road traffic accident involving two teenagers on an off road bike or scooter. And sadly, they died," Police and Crime Commissioner Alun Michael told BBC radio on Tuesday morning.
"It would appear that there were rumors, and those rumors became rife, of a police chase, which wasn't the case."
