Police official Anders Jansson said the fire started at an outside wall of the Swedish museum's cellar and spread into the facility, prompting the involvement of 25 firefighters from five area stations, the Swedish news agency TT reported Sunday.

Beer cans found near the cellar wall made police suspect arson may have been the cause of the blaze.

Jansson said due to the valuable artwork stored in the museum, firefighters had a difficult time extinguishing Saturday's fire. He added that an exhibit of stuffed animals in the museum contained the chemical formalin, commonly known as formaldehyde.

"It is a very complicated building in which to extinguish a fire. There are a large number of old paintings by Bruno Liljefors and the animals contain formalin. It is too early to say if any damage has been done," he told TT.