No injuries were reported at the site following the explosion, which occurred in the immediate vicinity of a Norwegian university campus. One person was arrested by police.

A loud explosion, which caused no injuries, was heard early Tuesday evening in Oslo, near Oslo Met, a higher education institution in the Norwegian capital, reports the Norwegian daily Aftenposten. According to witnesses quoted by the daily, "something resembling a grenade" was seen on the ground, while broken glass littered the roadway.

According to Norwegian police, initial investigations point to the possibility of a hand grenade being planted in the street. Investigators' main theory at this stage is that of a settling of scores between criminal gangs, the police said. One person has been arrested.

No further details were provided on the circumstances of the incident or the identity of the arrested suspect. According to public broadcaster NRK, the suspect is believed to be a minor. "We are looking for other suspects. We are assuming that there may be several people involved," Brian Skotnes said.

Gang war in Sweden

No casualties were reported by police at the site, which is located about 500 meters from the royal palace and the Israeli embassy. According to the daily Verdens Gang, a new detonation was heard around 9:45 p.m., and the police proceeded to defuse "an object," without giving further details.

Police reported at 9:11 p.m. that undetonated explosives were located at the scene and asked residents to stay away from windows, adding that other residents "should not enter the area." A large security perimeter was established and tram traffic was halted.

A police helicopter and drone flew over the area. This incident comes nearly a day after reports of drones flying near Oslo and Copenhagen airports. Norway has a low crime rate, but in recent months it has been hit by gang warfare in neighboring Sweden.