The PST told Agence France-Presse it had called in extra staff to assist police with the investigation.
Spokesperson Martin Bernsen stressed there had been “no change” to the threat assessment level in the Scandinavian country, which has been at three on a five-point scale since November 2024.
“We are now in close contact with, among other partners, the Oslo police district,” Bernsen said.
He refused to disclose whether any threats had been made against US interests in Norway prior to the explosion.
Shattered glass
Images in the media showed shattered glass in the snow outside the entrance to the embassy’s consular section, as well as cracks in a thick glass door and black marks on the ground at the foot of the door, presumably from the blast.
Investigators examined the scene overnight, while dogs, drones and helicopters were brought in to search “for one or more potential perpetrators,” Oslo police said.
“Police view such incidents in public spaces as very serious, and are investigating the case with substantial resources and high priority,” police said in a statement.
Security is normally high outside US embassies worldwide. It was not immediately known what security the Oslo embassy had at the time of the incident.
Oslo police commander Michael Dellemyr told TV2 police would “not comment on anything related to the type of damage, what it is that has exploded and similar details, beyond the fact that there has been an explosion” because “it is very early in the investigation.”
He later told TV2 that police “have an idea of the cause,” adding: “It appears to us that this is an act carried out by someone.”
Investigators questioned witnesses overnight, while TV2 reported that a bomb squad was seen at the scene.
Several hours after the blast, police declared the area around the building “safe” for residents and passersby.