"The complainants we know of at this time are boys. The case is at an early and intensive stage of the investigation, so I do not want to provide any further information. The suspect remains in custody, but the charge has been changed to assault of the normal degree," District Attorney Emma Haals says in a statement.
The man is suspected of aggravated assault.
The first arrest was made shortly after 11 a.m. on Sunday in the Sala Backe district of Uppsala, but police are not commenting on what happened at the scene.