The US embassy in Oslo has been hit by an explosion which caused minor damage but no injuries, according to Norwegian police. 

Eyewitnesses reported a loud explosion near the mission, in the Morgedalsvegen district of Oslo, about four miles outside the city center in the west of the Norwegian capital around 1 a.m. Sunday with smoke seen coming from the site of the blast. 

The Oslo police department told CNN that it was working with the embassy and there were no initial reports of injuries. 

Michael Dellemyr, who is leading the police response, told Norwegian media the explosion was at the public entrance to the building. Dellemyr told local television that police had an idea of the cause and that “it appears to us that this is an act carried out by someone.” 

In a statement to Norwegian broadcaster NRK, Minister of Justice Astri Aas-Hansen described it as “an unacceptable incident that is taken very seriously,” according to a translation.  

Investigators have been examining the scene, while dogs, drones, and helicopters were involved in the search for the perpetrators, according to Norwegian police.  

Police have called for information from the public, in particular anyone who might have seen anything in the area between midnight and 2 a.m. Sebastian Toerstad, 18, a high school student who drove past the embassy at the time of the incident told Reuters there was thick smoke on the street and some damage to the entrance of the mission. 

A search for the perpetrators is ongoing but no further explosive devices have been found in the area. 

The incident comes at a time of heightened security for US embassies and consulates following the bombing campaign by the U.S. and Israel against Iran, although it is not yet known whether the blast on Sunday was linked to events in the Middle East. 

The U.S. has pulled out staff from its missions across the Middle East as Iran steps up its strikes against American interests in the region in retaliation for Operation Epic Fury launched by President Donald Trump. On Tuesday, Iran struck the U.S. Embassy in Saudi Arabia and there was a similar incident involving the American mission in Kuwait.  

The U.S. has also issued travel warnings for Americans to the region, urging them to depart from more than a dozen Middle East countries because of “serious safety risks.”