LAST UPDATE | 8 hrs ago

POLICE IN NORWAY are investigating an explosion outside the US Embassy in Oslo, officials said.

Police received reports of a “loud bang” or explosion around 1am local time, Oslo police said in a news release. No injuries were reported.

The explosion was caused by some sort of incendiary device, according to Frode Larsen, leader of the Oslo police joint unit for investigation and intelligence.

Investigators believe the embassy was the target and are searching for the perpetrators and their motive.

Larsen said the embassy’s entrance had damage, but no arrests have been made.

“We are early in the investigation, but we are working based on multiple hypotheses,” Mr Larsen said in a statement.

“Given the current security situation, it is natural to consider whether this was a targeted attack on the American Embassy. However, we have not committed to any single hypothesis.”

Norwegian police and technicians attend at the U.S. Embassy in Oslo, Norway. Hans O. Torgersen / NTB Scanpix via AP Hans O. Torgersen / NTB Scanpix via AP / NTB Scanpix via AP

Local media reported that people nearby said the street was blanketed in thick smoke following the blast. Police are seeking to talk to witnesses.

A US official said the incendiary device was inside a backpack and detonated outside the entrance to the Consular Affairs office at the embassy.

The official spoke on condition of anonymity due to the sensitivity of the matter.

PST, the Norwegian police security service, called in additional personnel following the incident, but has not changed the country’s terror threat level, according to communication adviser Martin Bernsen.

Frode Larsen, head of the Joint Unit for Investigation and Intelligence, right, and Grete Lien Metlid, head of the Joint Unit for Operational Service giving a briefing to the media in connection with the potential explosion outside the U.S. Embassy in Oslo. Fredrik Varfjell / NTB Scanpix via AP Fredrik Varfjell / NTB Scanpix via AP / NTB Scanpix via AP

“This is an unacceptable incident that is being treated with the utmost seriousness,” said Astri Aas-Hansen, Norway’s minister of justice and public security.

“The police have stated that they are investigating the case with significant resources, and that nothing indicates the situation poses any danger to the public.”

The US Embassy in Oslo referred media inquiries to the US State Department, which said it was aware of the incident and was opening its own investigation.

“We thank the Norwegian authorities for supporting the investigation,” the statement said.