The restaurant was closed and nobody was hurt in the explosion.
“We know that the explosion was caused by an explosive device of unknown material, but we do not know whether it was placed inside or outside the building,” said police spokesman Anders Lycke.
Shots have been fired at the same restaurant on two occasions in the past year. The most recent attack was in January of this year.
Police say it is not known why the pizzeria has been the subject of attacks, nor is it known who is behind the shootings and bombing.
“We don’t want to add to speculation over who did this. We will continue during the day to carry out a technical examination and to question witnesses.”
The alert was raised after a passer-by saw smoke coming from the restaurant. No fire broke out, however, and after firefighters had checked the scene they handed over command to the police.