Investigation into Friday's blast, which injured around 20, is set to be extensive.

“It is absolutely incredible that nobody was seriously injured,” police press spokesperson Björn Öberg said.

Police have now limited street closures to the most severely-damaged sites.

“Assistance from NOA will arrive today and we are moving to a phase of pure investigation. It is a comprehensive job to put together all the leads and tip-offs we have had, so it will be a large investigation,” Öberg said.

No arrests have yet been made in connection with the explosion.

“We do not want to commit ourselves to a particular hypothesis,” Öberg said.

The explosion appears to have occurred just outside the apartment building which received the most damage.

That worse casualties did not result is down to pure luck, according to the police spokesperson.

Around 20 people received mild injuries in the explosion on Friday morning, with three being taken to the city’s University Hospital.

“They have splinters and cuts. Two patients are still here,” Region Östergötland medical officer Kim Berg said to press on Friday.

Either gas or explosives could have caused the blast, although explosives appear to be the most likely, Henric Östmark of the Swedish Defence Forces’ (Totalförsvaret) research unit told Corren.

“Most bomb explosions in Sweden in recent times have been smaller (than this),” Östmark said.

“We have to go quite far back in time to find something in Sweden with an explosion of this size,” he added.

Police said on Friday that they do not believe the explosion was linked to terror, but were not ruling anything out.

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