Oslo police said on 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 1.00am local time 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 broadcaster NRK.

"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. (AFP)


Edited by Aaron Tam