A teenager has reportedly been arrested after an explosion in central Oslo.
Police said they conducted a controlled detonation of a second explosive device found at the scene.
Brian Skotnes, the officer in charge, said that additional device appeared to be a “military-style” hand grenade.
The suspect is 13 years old, Norwegian media said.
No injuries were reported at the scene, near a university campus and 500 metres from the Israeli embassy.
In an unusual move, authorities sent an emergency message to Oslo residents’ mobile phones, warning them about the blast.
“We’ve apprehended one suspect and are intensively seeking more information as well as other people,” Mr Skotnes said.
“Our hypothesis is that it is criminals who have an agenda against other criminals, but we cannot rule out anything.”
The area is now safe, he added.
He declined to comment on the suspect’s age.
The incident comes almost a day after reports of drone sightings near the airports in Oslo and Copenhagen.
