Video caption Mohammad Rafiq tackled the gunman

A shooting at a mosque in Norway is being investigated as a possible act of terrorism, police say.

A gunman opened fire on the Al-Noor Islamic Centre, on the outskirts of the capital Oslo, on Saturday.

One person in the mosque managed to overpower the gunman and was injured in the process. The suspect was arrested after the attack.

Police also charged the suspect with murder after his 17-year-old stepsister was found dead in a separate location.

What do we know about the suspect?

The suspect has not yet been named, but police have described him as a white Norwegian citizen of "around 20 years old".

He was said to be "from the area" where the mosque attack took place, in the town of Baerum.

Rune Skjold, the acting chief of the police operation, said the suspect had been known to police before the incident but could not be described as someone with a "criminal background".

Mr Skjold said the man appeared to hold "far-right" and "anti-immigrant" views and had expressed sympathy for Vidkun Quisling, the leader of Norway's collaborationist government during the Nazi occupation.

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Norwegian media reported that the suspect was believed to have posted on an online forum hours before the attack. The post seemingly praised the gunman who killed 51 people in mosques in Christchurch, New Zealand, earlier this year.

The post also made references to a "race war", the reports said.

Officials say the suspect appears to have acted on his own. He did not want to "give an explanation to police".

The suspect has been charged with attempted murder over the shooting.

How did the attack unfold?

Only three people were inside the Al-Noor Islamic Centre at the time of the attack, preparing for the Muslim holiday of Eid-al-Adha the following day, a spokesman said.

Mosque director Irfan Mushtaq told local television network TV2 the suspect entered the building wearing a helmet and body armour, and armed with "two shotgun-like weapons and a pistol".

The gunman then opened fire before being overpowered by 65-year-old congregation member Mohammad Rafiq, who suffered minor injuries in the process.

Image copyright AFP Image caption The gunman was overpowered afer entering the mosque

"I suddenly heard shooting from outside. He started to fire towards the two other men," Mr Rafiq, a retired Pakistani Air Force officer, told Reuters news agency.

Mr Rafiq said he grabbed the attacker, held him down and wrestled the weapons from him.

The mosque had previously implemented extra security measures after the New Zealand attacks in March.

Norway tightly controls the purchase, possession and use of firearms. Permission to acquire a gun has to be obtained from the local police chief and is only given to those of "sober habits" who have reasonable grounds to need a weapon, according to the US Library of Congress.

Fully automatic weapons, some semi-automatic weapons and firearms disguised as other objects are banned, it says.

The Small Arms Survey estimates that there are 1,537,000 firearms in civilian possession in Norway.

How is the death connected?

Following the attack on Saturday, police said they had discovered the body of a young woman related to the suspect at a house in Baerum.

They confirmed on Sunday that the woman was the suspect's 17-year-old stepsister.

Officials are treating her death as suspicious and have opened an investigation. The alleged mosque attacker has been charged with murder in the case.

What has the reaction been?

The shooting has prompted debate over whether enough was being done to protect Norway's Muslim population.

Mosque director Mr Mushtaq said the government needed to take action.

"For so many years, the secret police says the Muslims are the biggest risk for this country, but if you look at those last two major incidents of terrorist activities, it's not Muslims who have done this," he said.

Video caption Prime Minister Erna Solberg said that working against hate speech was a priority.

Muslim organisation Islamic Council Norway described the attack as "the result of a long-lasting hate of Muslims that has been allowed to spread in Norway".

It said authorities had not "taken this development seriously".

Prime Minister Erna Solberg said on Twitter that Norway must fight hatred and anti-Muslim attitudes.

In separate comments, she said security had been ramped up for Sunday's Eid celebrations and that tackling hate speech was a priority.

"We are trying to combat this, but it's a challenge. I think it's a world-wide challenge in a sense," she said.

Official estimates from 2016 said some 200,000 Muslims lived in Norway, which has a population of about 5 million.