Smoke was seen rising from the area around the embassy compound, eyewitnesses told Norwegian daily Verdens Gang.
A loud blast was heard near the US embassy in western Oslo early on Sunday, triggering a large police response, investigators said.
It was not immediately clear what caused the blast, which happened at around 1 a.m. local time, or who was involved, the Oslo police department said in a statement.
“The police are in a dialogue with the embassy and there are no reports of any injured persons,” the statement said.
Smoke was seen rising from the area around the embassy compound, eyewitnesses told Norwegian daily Verdens Gang.
The embassy did not immediately respond to a request for comment outside of regular business hours.
