A gunman opened fire in central Oslo's bar area on the night between Friday and Saturday, killing two people — a man in his 50s and another in his 60s — and wounding more than 20.

The Norwegian security service called the attack an "Islamist terror act" during the capital's annual LGBT+ Pride festival. A suspect is in custody.

The crime scene included the London Pub, popular with the city's LGBT+ community, but police investigators have said it was unclear whether the motive of the assailant was hatred toward sexual minorities.

Norwegian Prime Minister Jonas Gahr Støre said in a speech during Sunday's memorial service that "the shooting in the night hours put an end to the Pride parade, but it did not stop the fight and the efforts to fight discrimination, prejudice and hatred."

He also addressed Norway's Muslim community.

"I know how many of you felt when it turned out that the perpetrator belonged to the Islamic community. Many of you experienced fear and unrest."

"You should know this: We stand together, we are one community and we are responsible for the community together," Gahr Støre said during the church service, which was also attended by Crown Princess Mette-Marit.

Norwegian media have identified the suspect as 42-year-old Oslo resident Zaniar Matapour, who arrived in Norway with his family from a Kurdish part of Iran in the 1990s.

The Norwegian domestic security agency PST said Saturday it first became aware of the suspect in 2015 and later grew concerned he had become radicalized and was part of an unspecified Islamist network.

On Sunday, Norwegian media outlets reported that Matapour allegedly was in close contact with an Islamic extremist living in Norway who has been known to the Norwegian police for a long time.

The extremist, identified as Arfan Bhatti, is known among other things for his strong anti-gay views, Norwegian public broadcaster NRK said.