One person has been injured after a shooting at a mosque just outside Oslo, Norwegian police said on Saturday, adding that a suspect had been arrested.
The body of a young woman related to the suspect was later found in a home in the suburb of Baerum where the shooting took place earlier in the day.
Investigators have opened a murder investigation over the woman's death.
The suspected shooter is believed to have acted alone and is young and white, the police said.
"It is a Norwegian young man, with a Norwegian background. He lives in the vicinity," Oslo police spokesman Rune Skjold told a press conference.
The shooting took place at the Al Noor Islamic Centre and the victim has been identified in media reports as a 75-year-old worshipper.
"The man carried two shotgun-like weapons and a pistol. He broke through a glass door and fired shots," the mosque's director Irfan Mushtaq told TV2.
Members of the mosque overpowered the shooter, wearing body armour, before the police arrived, Mr Mushtaq said.
The incident took place at around 4pm local time on the day before the celebration of Eid Al Adha.
Police said the extent of the victim's injuries are not yet known.
In 2011, a far-right extremist with anti-Muslim beliefs killed 77 people in two terror attacks in Norway, most of whom were young people attending a summer camp organised by the Labour Party's youth wing.
Anders Breivik's attack was the deadliest in the Scandinavian country since the Second World War.
The mosque in Norway has the same name as the Islamic centre in Christchurch, New Zealand, which experienced a deadly attack by a far-right gunman in March.
The Christchurch shooting suspect wrote a hate-filled manifesto before the attack claiming he was influenced by Breivik.