The brothers intended to kill people and cause extensive material damage when they detonated "a powerful bomb" at the American embassy in Oslo.
Police prosecutor Christian Hatlo said this at a press conference, adding that police are working on several hypotheses regarding motive.
"One is whether it involved an order from a government actor."
One of the men admits to having placed a bomb at the embassy.
"He admits that he placed the bomb there, which links him to the scene. He has been questioned by the police. He has explained what happened and I have no further comments at this time," his lawyer Øystein Storrvik told Norwegian TV2.
The three are all around 20 years old and live in Oslo, and are Norwegian citizens of Iraqi origin. None of them have previously been known to Norwegian police.
No one was injured in the explosion, which occurred at 1:03 a.m. Sunday. The explosion caused minor damage.
