The late-night shooting led police to call off an LGBTQI+ pride march planned for Saturday in Oslo.
Police in Norway charged a man with "terrorism" Saturday, after a late-night shooting in central Oslo left two dead and dozens more injured.
An LGBTQI+ march in the Norwegian capital scheduled for Saturday was cancelled following the fatal attack, which hit two bars, including one gay club.
Two people were left dead and at least 21 more have been injured, including 10 seriously.
The alleged perpetrator, whose identity has not been disclosed, is a 42-year-old Norwegian of Iranian origin, police said Saturday.
Norway's security services (PST) have suggested they are treating the attack as an act of "Islamist terrorism," although they have noted "difficulties" with the suspect's mental health.
Head of the PTS, Roger Berg, said the suspect "has a long history of violence and threats". He has been on the organisation's radar over radicalisation concerns and his membership of an extremist Islamist network since 2015.
Following an interview with the man last month the PTS concluded he no longer had "violent intentions", according to Berg.
The shooting, which occurred at 1:00 a.m. local time (23:00 GMT), took place outside the Per på hjørnet pub, where two deaths were reported, according to local media.
The attacker then moved onto an adjoining gay club, the London Pub, in downtown Oslo.
"There are reasons to believe that this is a hate crime”, said Oslo police official Christian Hatlo, referring to the nature of the places targeted.
The suspect's lawyer, John Christian Elden said his client would undergo "judicial observation" to determine his mental state.
Police requested organisers to call off an LGBTQI+ march planned for Saturday afternoon, while rainbow flags have been placed near the scene of the attack as a sign of solidarity.
After "clear advice and recommendations from the police", "all events related to Oslo Pride are cancelled," the pride organisers wrote in a Facebook post, imploring "anyone who had planned to participate in or watch the parade, not to show up."
The suspect, whose identity has not been disclosed, was known to Norway's intelligence services, Hatlo told reporters at the Saturday morning press conference.
He was arrested five minutes after the first reports of the shooting at 1:19 a.m. (23:19 GMT).
Police had dealt with the suspect in the past for minor acts, such as carrying a knife, alongside a conviction for possessing narcotics.
An automatic weapon and handgun were seized by police at the scene of the attack, which were described as "old" by Hatlo.
Civilians made a "heroic contribution" according to police, helping capture the suspect and providing first aid to victims.
One witness told the Verdens Gang (VG) newspaper that it was "a scene of war", adding there were "plenty of injured people on the ground" with "head injuries".
Norwegian police have beefed up their presence in the capital to deter possible other incidents.
"It is estimated at this stage that there was only one person" behind the shooting "but nothing can be said with certainty so early," said inspector Tore Soldal.
Prime Minister Jonas Gahr Støre condemned the shooting as a "cruel and deeply shocking attack" in a Facebook post.
"My thoughts go out to those affected and their relatives," he wrote. "We still don't know what was behind this horrible act, but to the homosexuals who are now scared and in grief, I want to say, we all stand with you."
Announcing the cancellation of the Oslo Pride March, organiser Kristin Haugsevje said they were following the police’s recommendation to "take care of each other".
"We are sending warm thoughts and love to next of kin, those who were wounded, and others affected."
"We will soon be proud and visible again, but today, we will share our Pride celebrations from home," she added.