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The meeting, the first of its kind, in Paris overnight saw all of the major technology companies, 17 countries and the European Commission sign up to the call initiated by New Zealand Prime Minister Jacinda Ardern and French President Emmanuel Macron, in the wake of the Christchurch attack in March that killed 51 people.
The action plan asks tech companies to review the operation of their algorithms that are driving users towards or amplifying terrorist content online and find ways to intervene earlier.
In order to try and prevent an attack like the one in Christchurch from happening again, tech companies have agreed to share the effects of algorithim secrets with each other.
Ms Ardern has called on them to report progress regularly to governments.
At a news conference, Ms Ardern described the agreement as "day one" in the change the world needed.
New Zealand and global investors worth more than $NZ5 trillion are uniting to put pressure on companies who have signed up to the Christchurch Call.
Launched alongside the summit in Paris overnight, the New Zealand Super Fund has coordinated the investor group, worth more than 15 times the GDP of the New Zealand economy.
The group wants to get Facebook, Twitter and Google - who all have social media platforms - to strengthen controls that will prevent the live streaming and distribution of objectionable content.
They plan to raise concerns with the companies' board and management on these issues.
The investor group is made up of 55 funds - 27 from New Zealand and 28 from across the globe.
New Zealand banks, ACC, and global trusts and pension funds make up the group.
The United States has snubbed the Christchurch Call summit by not attending or endorsing the agreement.
In a statement from the White House, a spokesperson said the US stood with the international community in condemning terrorist and violent extremist content online in the strongest terms.
But it said the US was not currently in a position to join the agreement, although it supported its the overall goals.
It cited freedom of expression and freedom of the press as reasons it would not be joining the agreement, and said promoting credible, alternative narratives was the best way to defeat terrorist messaging.
A day before the accord was signed, Facebook announced it was tightening rules on live streaming in response to the Christchurch terror attack and introducing a new would be a "one-strike policy" banning those who violate new Facebook Live rules.
Ms Ardern said Facebook's move was a first step. "We look forward to further work to stop social media being perverted as a tool for terrorists and preserving it instead as a means for individuals and communities to connect."
Signatories to the 'Christchurch Call':
Australia, Canada, European Commission, France, Germany, Indonesia, India, Ireland, Italy, Japan, Jordan, the Netherlands, New Zealand, Norway, Senegal, Spain, Sweden, United Kingdom.
Companies: Amazon, Daily Motion, Facebook, Google, Microsoft, Qwant, Twitter, YouTube.