Two people were reported injured, one seriously, on Sunday in a blast outside the entrance to a metro station in a southern Stockholm suburb, police said.
The police said there was no reason to believe the event was terrorism-related.
The seriously injured person was reported to be a man in his 60s.
He picked up an item from the ground that exploded, police said. He has been taken to hospital, spokesman Sven-Erik Olsson added.
A woman in her mid 40s was also taken to hospital, but her injuries were not described, local media reported.
Police have cordoned off an area outside the entrance to the metro station Varby Gard, and were investigating the incident. The station has been closed.
Tabloids Aftonbladet and Expressen reported that the blast was thought to have been caused by a hand grenade, but police spokesman Sven-Erik Olsson declined to confirm the reports.