"At the moment, this has been classified as vandalism that endangers the public (allmänfarlig ödeläggelse)," Michael Carlzon, Malmö police spokesman, told Sveriges Television (SVT). "Usually when it comes to explosives, it is classified as aggravated assault, but that could change."
The police said there were no registered threats against the man or his family. The victim was recently outed by the tabloid Expressen, which published the names of several Sweden Democrat party representatives who had left controversial comments on sites such as Avpixlat. Among other statements, he said Swedes had to take up arms to "defend their country", SVT reported.
"The man in the family represents the Sweden Democrats, but we don't have a motive nor a suspect," Carlzon said.
Forensic officers scoured the blast-damaged door and the flat for clues, while police spoke with neighbours.
The Expressen newspaper reported that the family had been taken to a safe location by the police.
Sweden Democrat party secretary Björn Söder told SVT the blast could be due to the recent revelations made public by Expressen and the leftwing Researchgruppen team of investigative reporters.
"It's easy to think this is a consequence of the Expressen campaign, where a number of Sweden Democrats were hung out to dry," Söder told SVT.