An explosion rocked the U.S. embassy premises in western Oslo in the early hours of Sunday, leaving some damage at the consular entryway but no reported casualties, Norwegian authorities said.
The blast was heard at roughly 1 a.m. local time (0000 GMT) inside the embassy compound. Witnesses described seeing a heavy plume of smoke rising from the site shortly after the sound of the detonation.
"There was a very thick layer of smoke on the street," said Sebastian Toerstad, 18, a high school student who drove past the embassy around the time of the incident. "There was some damage to the entrance," he added.
Oslo police indicated the explosion occurred at the entry to the consular section of the embassy. Two police technicians, observed wearing white overalls, later worked at the scene as part of the response.
"Investigations have been carried out at the scene with the aid of dogs, drones and a helicopter, searching for one or more potential perpetrators," the Oslo police department said in a statement.
Police said no additional explosive devices had been located in the immediate area following initial searches. Authorities employed canine units, aerial drones and a helicopter to survey and secure the perimeter while collecting evidence and seeking possible suspects.
The embassy did not answer a request for comment outside of regular business hours. The U.S. State Department also did not immediately provide a response to a request for comment.
Officials described the physical damage as limited and confirmed there were no injuries among embassy staff, visitors or passersby. Investigators remain at the scene conducting forensic and security checks as they work to determine the circumstances surrounding the explosion.
As of the latest updates from police, searches of the surrounding area had not turned up further devices, and law enforcement resources remained deployed to ensure public safety and to advance the ongoing inquiry.