Ammon News - Norwegian police said on Tuesday they were investigating a blast on a street in central Oslo and later conducted a controlled detonation of a second explosive device found on the site, adding that a suspect had been apprehended for questioning.

There were no reports of injuries at the location, in the immediate vicinity of a university campus and some 500 metres (546 yards) from the royal palace and the Israeli embassy.

In a rare step, authorities sent an emergency message to Oslo residents' mobile phones, warning them about the blast.

The incident comes a day after reports of drone sightings near Oslo's and Copenhagen's airports.

Reuters