Wellington, Apr 8 (IANS): A Royal Commission of Inquiry will begin probing the March 15 Christchurch terror attacks that left 50 people dead in two mosques on May 13, New Zealand Prime Minister Jacinda Ardern said on Monday.

"The Royal Commission plays a critical role in our ongoing response to fully understand what happened in the lead up to the attack and to ensure such an attack never happens again," Efe quoted Ardern as saying at a press conference here.

The lone gunman, Australian Brenton Tarrant, was arrested shortly after he massacred the worshippers at the city's Al Noor Mosque and the Linwood Islamic Centre.

He is in custody facing 50 murder charges and 39 attempted murder charges.

"The government will ensure no stone is left unturned as we examine as quickly as possible how the March 15 attack happened, what could have been done to stop it and how we can keep New Zealanders safe," Ardern said.

The attack has forced intelligence and security agencies to rethink surveillance of individuals and right-wing extremist groups and has triggered a debate over the responsibilities of social media networks.