Il Nuovo Postiglione - Three brothers arrested over US embassy blast in Oslo

Police prosecutor Christian Hatlo told a press conference the brothers, who were Norwegian citizens of Iraqi origin, had been arrested in Oslo 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, 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.

Oystein Storrvik, a lawyer for one of the suspects, told broadcaster TV 2 that his client had admitted "to being involved in the case".

"He admits that he placed the bomb there," Storrvik told the broadcaster.

Storrvik added that his client had been questioned by police.

"He has explained what happened, and I have no further comments at this time," he said.

- 'Proxy actors' -

While none of the brother were previously known to police, Hatlo said investigators were not ruling out links to "criminal networks".

In its annual threat assessment, 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 1:00 am (0000 GMT) on Sunday at the entrance to the embassy's consular section.

On Monday, two images were released from surveillance camera footage showing 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 killed 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.

E.Scozzafava--INP