The US embassy in Oslo has been hit by an explosion in the early hours of the morning, Norway's police say.

"Large resources" were sent to the area in the Norwegian capital at about 01:00 local time on Sunday (00:00 GMT), police said.

"The police are in dialogue with the embassy and no injuries have been reported," a statement said.

It added that there was currently "no information about exactly what happened or who may be involved".

The embassy sustained minor damage. The diplomatic mission's US employees have not commented.

Michael Dellemyr, who is leading the police response, told Norway's public broadcaster NRK the explosion was at the public entrance to the building.

He said police officers had conducted searches in the area around the embassy in the Morgedalsvegen district of Oslo, about 7km (4 miles) outside the city centre.

He said the police had also issued an appeal for information from anyone who may have seen or heard anything about the incident.

Photos posted on social media later showed shattered glass in the snow outside the entrance to the consular section of the building, cracks in a glass door as well as dark marks on a tiled floor.

Norwegian authorities described the incident as "unacceptable", with Foreign Minister Espen Barth Eide stressing that "the security of diplomatic missions is very important to us".

He added that he had contacted US embassy chargé d'affaires Eric Meyer regarding Sunday's incident.