A Royal Commission of Inquiry is needed into New Zealand's security and intelligence agencies following the Christchurch terror attacks, the National Party leader says.
Simon Bridges is also calling for a review of security legislation to ensure New Zealanders are kept safe as the security risk had "changed".
Mr Bridges said the Royal Commission would need to ask hard questions about whether security and intelligence agencies had their focus in the right places.
"A Royal Commission is the only suitable level of inquiry to ensure this is investigated thoroughly and independently," Mr Bridges said.
"We need to understand whether this could have been prevented."
Mr Bridges said the review of security legislation was needed to see if the security agencies needed greater powers.
He said a decision made by the former National government in 2013 to abandon Project Speargun, which would have scanned internet traffic coming into New Zealand, should be reconsidered.
That project "would have given an extended degree of protection to all New Zealanders. Similar systems are used in other jurisdictions," he said.
"It's never easy to balance the rights of privacy against security but where we draw the line, must now be reconsidered."
Mr Bridges said an inquiry should not be used by the government to delay making decisions on how best to keep people safe.
"Our security risk has now changed and New Zealanders need to be kept safe. The Royal Commission should look at the past, and parliament should get on with actions for the future."