The New Zealand Prime Minister said the inquiry would look at 'what could have or should have' been done to prevent the attack.
New Zealand Prime Minister Jacinda Ardern on Monday ordered an independent judicial inquiry into the Christchurch mosque attacks, saying she wanted to know how a gunman shot dead 50 people on March 15.
"It is important that no stone is left unturned to get to how this act of terrorism occurred and how we could have stopped it," Ardern told reporters, adding the inquiry would include intelligence services and police.
Fifty people were killed in the March 15 attack on Christchurch's Masjid al Noor and Linwood Masjid when a lone gunman opened fire during Friday prayers.
Ardern said a royal commission - the most powerful judicial probe available under New Zealand law - was needed to find out how a single gunman was able to kill 50 people in an attack that shocked the world.
The details of the commission, including its duration, will be finalised this week, she said.
"What I can say, today, is that there will be a focus on whether our intelligence community was concentrating its resources appropriately and whether there were
New Zealand's spy agencies have faced criticism in the wake of the attack for concentrating on the threat from Islamic extremism.
Instead, the victims were all Muslims and the massacre was allegedly carried out by a white supremacist fixated on the belief that Muslims were "invading" Western countries.
"One question we need to answer is whether or not we could or should have known more," Ardern said.
"New Zealand is not a surveillance state ... but questions need to be answered."
Ardern ruled out New Zealand re-introducing the death penalty for accused gunman Brenton Tarrant, 28, who was arrested minutes after the attack on the mosques and has been charged with murder.
Ms Ardern also announced Monday that a long-awaited trip to China will take place next week, but had been shortened in the wake of the Christchurch mosque killings.
She is to travel to Beijing on Sunday then hold a full day of meetings Monday with the leaders of New Zealand's largest trading partner, including President Xi Jinping, before returning home the next day.
She said she did not want to spend too long away from New Zealand as it continues to mourn the March 15 shootings at two Christchurch mosques that claimed 50 lives.
"It was originally intended to be a longer visit, including a business delegation, but under the circumstances that did not seem appropriate to be away for longer," she told reporters.
It will be Ardern's first visit to China since she was elected in late 2017 -- an unusually long wait for the leader of a nation that signed a pioneering free-trade deal with Beijing in 2008.
The gunman livestreamed the attack online, although New Zealand has outlawed the footage as "objectionable content".
Ms Ardern reiterated her believe it should not be aired.
"That video should not be shared. That is harmful content," she said when questioned about Turkish President Recep Tayyip Erdogan showing excerpts of the footage at campaign rallies for local elections this month.
Mr Erdogan had angered both Wellington and Canberra with campaign rhetoric about anti-Muslim Australians and New Zealanders being sent back in "coffins" like their grandfathers at Gallipoli, a World War I battle.
New Zealand Foreign Minister Winston Peters travelled to Istanbul to meet Erdogan and address an emergency meeting of the Organisation of Islamic Cooperation.
Peters said OIC members were full of praise for the support New Zealand had offered its small, tight-knit Muslim community in the wake of the killings.
"A number of them were weeping and sobbing at the demonstration (of support) by non-Muslim New Zealand towards the Muslim victims," he told reporters.
"It was dramatic and I was told by countless ministers that they've never seen anything of that type."
The body of an Indian student killed in the Christchurch mosque attacks, meanwhile, was returned Monday to her grieving family in Kochi, where relatives remembered a bright young woman dedicated to her studies.
Ansi Alibava, 25, was the first of at least five Indians shot dead on March 15 to be repatriated.
The family planned to hold a funeral ceremony for the masters student in their nearby hometown of Kodungallur.
The prime minister has announced a national memorial service will be held on Friday, with thousands expected to turn out again in solidarity for the local Muslim community.
They were able to return to the scene of the tragedy on Saturday, a week and a day after the attacks that also injured 50 people.
"The service will be a chance to once again show that New Zealanders are compassionate, inclusive and diverse, and that we will protect those values," she said.
The service will be broadcast live to events in Auckland, Wellington and Dunedin.
Foreign delegations are expected, including a representative of the British royal family.
It's rumoured to be Prince William who has visited Christchurch several times.
A vigil was held on Sunday night for the victims, where the call was for continued love and unity as many asked what will come next.
Interim measures have banned semi-automatic firearms like those used in the attack until legislation is introduced, likely around April 11.
The alleged gunman, 28-year-old Australian Brenton Tarrant, has been transferred from Christchurch and is now believed to be held in a maximum security prison in Auckland.
He has no access to television, radio or newspapers and no approved visitors.
Tarrant is charged with one count of murder but is expected to face more charges. He's due to return to court on April 5.