The alarm was received by the police at 02:13 on Thursday night about a loud bang in a residential area in central Nyköping.
The police were able to ascertain at the scene that something had detonated at the gate of an apartment building.
– There are no injuries and no material damage to nearby houses, says Camilla Larsson, officer on duty at the police.
The site has been cordoned off pending the National Bomb Squad.
– We have a good resource at the scene and have also taken resources from other parts of the police area. Now we are working on knocking on doors in the area to get more information.
The police also have contact with those who live in the building.
A preliminary investigation into attempted murder has been launched. The criminal classification may change.
There are currently no suspects or arrests.
The text is updated.