The explosion took place at a row house at 02:30 and when the police arrived at the scene, a suspicious object was discovered.
The decision to cordon off the area was not made until after 06:00 on Wednesday morning, after the national bomb squad had checked the object and deemed it harmless.
According to information provided to VLT, it is a hand grenade that exploded.
We will conduct a technical investigation, which will show what detonated. Until then, we cannot confirm what it is, says the police's press spokesperson Maria Hall.
A door belonging to the row house was damaged in the incident. The police have had large cordons in the area and collected witness statements.
We have held interrogations and collected other material that we will go through, says Stefan Larsson, press spokesperson at the police.
The police have initiated a preliminary investigation into general endangerment and serious crime under the law on fire hazardous and explosive goods.
No one has been arrested yet.
