A gunman armed with multiple weapons opened fire in a mosque near Oslo on Saturday, injuring one person before being overpowered by an elderly worshipper and arrested, Norwegian police and witnesses said.
Hours after the attack, the body of a young woman related to the suspect was found in a home in the suburb of Baerum where the shooting took place earlier in the day, police said Saturday evening.
Investigators are treating her death as suspicious and have opened a murder probe.
The head of the mosque described the assailant as a young white man dressed in black and said he was wearing a helmet and bulletproof vest.
He said only three people had been inside the al-Noor Islamic centre at the time of the attack.
Police were alerted to the shooting shortly after 4:00 pm (1400 GMT).
Officers first reported that a victim had been shot, but later clarified one person had sustained "minor injuries" and that it was unclear if they were gunshot wounds.
Police said the suspect appeared to have acted on his own.
"It is a Norwegian young man, with a Norwegian background. He lives in the vicinity," Oslo police spokesman Rune Skjold had told a press conference earlier Saturday.
Skjold added that the suspect had been known to police before the incident but could not be described as someone with a "criminal background".
The man -- who was in his early twenties -- was taken into custody, police said in a press release carried by Norwegian media, adding that he would be interrogated "on the events at the mosque and the homicide".
Norway was the scene of one of the worst-ever attacks by a right-wing extremist in July 2011, when 77 people were killed by Anders Behring Breivik.
"One of our members has been shot by a white man with a helmet and uniform," Irfan Mushtaq, head of the mosque, told local media.
Mushtaq said that the man had carried multiple weapons, but that he had been subdued by a member of the mosque.
Mushtaq himself had arrived at the scene shortly after being alerted about the gunman, and had gone to the back of the building while waiting for police to arrive.
"Then I see that there are cartridges scattered and blood on the carpets, and I see one of our members is sitting on the perpetrator, covered in blood," Mushtaq told Norwegian newspaper VG.
He said the man who apparently overpowered the shooter was 75 years old and had been reading the Koran after a prayer session.
According to Mushtaq, the mosque had not received any threats ahead of the shooting.
The attack took place on the eve of the Muslim celebration of Eid Al-Adha, marking the end of the Muslim pilgrimage Hajj.
Police said Saturday they would be sending out more officers so that those celebrating would "be as safe as possible".
There has been a recent spate of white nationalist attacks in the West, including in the United States and in New Zealand where 51 Muslim worshippers were killed in March in shootings at two mosques in the city of Christchurch.
The al-Noor Islamic centre in Norway shares its name with the worst affected mosque in the New Zealand attacks.
Local Norwegian paper Budstikka said it had contacted the mosque in March after the Christchurch massacre and that officials there had said security would be tightened.
The suspect in the Christchurch killings wrote a hate-filled manifesto in which he said he was influenced by far-right ideologues including Breivik.
Breivik detonated a massive bomb in Oslo that killed eight people and then opened fire on a gathering of the Labour Party's youth wing on the island of Utoya, killing another 69 people, most of them teenagers.
Norwegian police said they were aware that Saturday's suspect had been active online prior to the shooting.
Broadcaster TV2 reported they had learned the identity of the man and located a post to an online forum from someone using the same name, posted only hours before the attack.
The post seemingly praising the New Zealand attacker and ended with the words "Valhall awaits".