Norwegian police said an explosive device had been thrown at the diplomatic compound Sunday morning

Norwegian police are investigating an explosion outside the US Embassy in Oslo as a possible act of terrorism. The incident occurred amid heightened security for American diplomatic missions following the US-Israel air war with Iran.

The blast happened at around 1 a.m. on Sunday and caused minor damage to the entrance of the diplomatic compound. An explosive device appears to have been thrown at the building, Grete Metlid, head of operational services at Oslo police, said during a press conference. Photographs from the scene show broken glass and fallen lamps near the entrance.

Shortly after the explosion, a video appeared on the embassy's Google Maps page showing Iran's slain Supreme Leader Ayatollah Ali Khamenei accompanied by a message in Arabic: "God is great. We are the victors." Police said they were aware of the clip and are examining it as part of the investigation.

"One of the hypotheses is that it is an act of terrorism," Frode Larsen, head of the Oslo police investigation and intelligence unit, told NRK.

Norway's domestic security service PST has joined the probe and is investigating the incident as a high priority, with security tightened around the site. No arrests have been made so far.

American diplomatic missions worldwide have been placed on high alert following joint US-Israeli airstrikes on Iran that began on February 28. Iran responded by launching missiles and drones at American bases across the Middle East and at Israel.

US diplomatic missions in Dubai and Riyadh have reportedly been targeted by Iranian drones, prompting the State Department to close embassies in Saudi Arabia, Lebanon, and Kuwait, and to urge American citizens to leave the Middle East.

At least 10 people were killed in Karachi, Pakistan, when US Marines opened fire on protesters attempting to storm the American consulate on March 1.

More than 32,000 Americans have returned from the Middle East since the start of the conflict, according to the State Department.

President Donald Trump has demanded an "unconditional surrender" from Iran as the US military reportedly braces for a weeks-long campaign.