The entrance to the building, a well-known sculpture and several windows were damaged as a result of the blast but noone was hurt.
At a lunchtime news conference, Thursday, the police said that it was too early to say what caused the explosion or any possible motives for it.
"It is another cowardly attack on society and democracy," Police chief Patric Heimbrand told SVT News.
The southern city of Landskrona has experienced several instances of violent crime associated with criminal networks this summer.
Torkild Strandberg, chair of the municpal council, called the explosion "totally unacceptable". Speaking to Swedish Radio, the liberal politician said; "I'm terribly upset and I think it's a feeling I share with most of the staff here at City Hall and the Landskrona residents I met this morning. This is a completely unacceptable event."