Swedish police on Tuesday were investigating a riot that broke out overnight in a predominantly immigrant suburb in Stockholm after officers arrested a suspect on drug charges.

The clashes started late Monday when a police car arrested a suspect and people started throwing stones at them in Rinkeby, north of Stockholm. Unidentified people, including some wearing masks, also set cars on fire and looted shops.

One officer was slightly injured when a rock hit his arm and one person was arrested for throwing rocks, police spokesman Lars Bystrom said Tuesday.

Some civilians who tried to stop the looters were also assaulted, he added.