Norwegian police said on Wednesday that three brothers had been arrested on suspicion of a “terrorist bombing” over a weekend explosion at the US embassy in Oslo, which caused minor damage but no injuries.

Police prosecutor Christian Hatlo told a press conference the brothers, who were Norwegian citizens of Iraqi origin, had been arrested in Oslo around 3:30pm local time (2:30pm GMT), and that police were investigating the motive.

“We are still working from several hypotheses. One of them is whether this is an order from a government entity,” Hatlo said.

“This is quite natural given the target — the US embassy — and the security situation the world is in today,” he said.

Hatlo said the investigation would seek to clarify exactly what roles the brothers, who were in their 20s and not previously known to police, had played.

“We believe that one of them is the person who placed the bomb outside the embassy and that the other two were complicit in the act,” Hatlo told reporters.

Hatlo also said that they were not ruling out links to “criminal networks”.

‘Proxy actors’

In its annual threat assessment, the Norwegian security service PST said last month that Iran, which it considers one of the main threats to the country, could rely on “proxy actors,” including “criminal networks,” to commit acts.

On Tuesday, Iran’s ambassador in Oslo denied any involvement by his country in the embassy explosion.

“It is unacceptable that we are being singled out,” Alireza Jahangiri told Norwegian newspaper Verdens Gang.

According to police, the perpetrators of the bombing, described as “powerful”, may also have acted out of their own motives.

US embassies have been placed on high alert in the Middle East due to American strikes on Iran. Several have faced attacks as Tehran responds by targeting industrial and diplomatic facilities.

The blast took place at around 1am (12am GMT) on Sunday at the entrance to the embassy’s consular section.

On Monday, two images from surveillance camera footage of a suspect dressed in dark clothing with a hood over his head and wearing a backpack.

Roughly at the time the incident occurred, a video had been uploaded to the Google Maps page for the US embassy.

The video, which has since been taken down, appeared to show Iran’s late supreme leader Ayatollah Ali Khamenei, who was assassinated on the first day of the US-Israeli strikes in Iran.

According to Norwegian public broadcaster NRK, the person who uploaded the video wrote in Persian: “God is great. We are victorious.” Police have also opened an investigation into this.