A dozen police officers and a member of the public were injured in a protest against a decision to allow several right-wing demonstrations to go ahead in the southern Swedish city of Örebro, broadcaster SVT reported on Saturday.
Around 500 people participated in the demonstration on Friday, which also saw several police vehicles set alight.
A second protest was held in the capital Stockholm, where stones were thrown.
Tensions have risen since a well-known right-wing extremist secured permission to hold a gathering at which he planned to burn a copy of the Koran.
A further demonstration planned in the southern town of Landskrona on Saturday was moved at the last minute to the city of Malmö due to the rioting.
Around 60 people gathered in Landskrona nonetheless, leading to clashes.
