“Bomb disposal officers carried out a controlled explosion overnight Saturday,” a Norwegian police statement said.
Police cordoned off part of the busy Grønland district and evacuated local bars and restaurants after the crude device — described as having the capacity to cause only limited damage – was discovered Saturday evening.
Norway's PST police security agency is investigating.
There were no immediate further details.
The device was discovered a day after four people were killed and 15 injured after a truck rammed into shoppers in Stockholm. Swedish police have detained a 39-year-old Uzbek man in connection with that incident.