Oslo police said Sunday an explosion at the US embassy in Norway overnight that caused no injuries and minor material damage may have been an act of terror, but stressed police were also investigating other motives.
Police did not provide details about what caused the blast, which occurred around 1:00 am (0000 GMT) at the entrance to the embassy's consular section, saying only that an "explosive device" had been used.
Shattered glass could be seen in the snow outside the entrance, as well as cracks in a thick glass door, overhead lamps dangling from wiring, and black marks on the ground at the foot of the door, presumably from the blast.
"One of the hypotheses is that it is an act of terrorism," Frode Larsen, the head of the police's joint unit for investigation and intelligence, told public broadcaster NRK in an interview.
"But we are not completely stuck on that. We have to be open to the possibility that there may be other causes behind what has happened," he said, speaking on the sidelines of a press conference.
Police were searching for the perpetrators but had "no suspects" yet, Larsen told the press conference.
US embassies have been placed on high alert in the Middle East over American military operations in Iran and several have faced attacks as Tehran hits back at industrial and diplomatic targets.
Investigators in Oslo have not ruled out a possible link to the war in the Middle East.
"It is natural to see this in connection with the current security policy situation," Larsen said, adding that police have increased security at the scene after the attack.
Norway's Foreign Minister Espen Barth Eide earlier said he and Justice and Public Security Minister Astri Aas-Hansen had been in contact with US embassy charge d'affaires Eric Meyer.
The pair "expressed that this is an unacceptable act that we take very seriously", he said in a statement.
"The security of diplomatic missions is extremely important to us."
The Norwegian security service PST told AFP it had called in extra staff to assist police with the investigation.
Spokesman 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.
He refused to disclose whether any threats had been made against US interests in Norway prior to the explosion.
Investigators examined the scene overnight, while dogs, drones, and helicopters were brought in to search for the perpetrators, Oslo 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.
Several hours after the blast, police declared the area around the building "safe" for residents and passersby.
Police urged the public to report any tips or unusual observations from the area between midnight and 2:00 am (2300 GMT and 0100 GMT).
