An explosion rocked the grounds of the US Embassy in Oslo early Sunday morning, causing minor damage but no injuries, Reuters reports, citing Norwegian police.

Witnesses said the explosion was heard at the embassy in the western part of Oslo around 1:00 AM local time (00:00 GMT), with smoke rising from the area.

Oslo police said the explosion occurred at the entrance to the consular section. Two police technicians in white overalls were later spotted at the scene.

According to police, no other explosive devices were found in the area.

"Investigative measures were carried out at the scene using dogs, drones and a helicopter in search of one or more potential perpetrators," the Oslo police department said.