Police in Norway have cordoned off the area around the US embassy in Oslo after an explosion was reported there.

"Large resources" were sent to the area at about 01:00 local time (midnight GMT), police said.

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

"There is currently no information about exactly what happened or who may be involved," police added.

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

The embassy sustained minor damage, media reports say.

The US embassy is located in the Morgedalsvegen district of Oslo, about 7km (four miles) outside the city centre.