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On her way back from signing the Christchurch Call to Action in Paris, Ms Ardern spent the day signing an upgraded trade deal in Singapore, which this week passed a new law to fight fake news.
The law empowers the Government to fine tech companies if they fail to take down content the Government believes is untrue and harmful.
Its passage sparked an outcry that the Government was giving itself self-serving Orwellian powers, though the Government said it was about blocking lies and keeping public debate honest.
Canadian Prime Minister Justin Trudeau, who signed the Call to Action in Paris, is also considering fines for social media outlets if they do not combat fake news.
The harm from online misinformation campaigns has been in the spotlight since Russian agents were revealed as using Facebook to manipulate public opinion, including about US politics.
But Ms Ardern said she had no plans to broaden the Christchurch Call, which asks signatories to abide by the principles of free speech and an open, secure internet.
The call also asks countries to ensure societies are resilient against violent extremism, but it does not cover wider issues of misinformation because they are greyer free-speech areas.
Ms Ardern did not say whether she thought Singapore's new law was consistent with free-speech principles, but Singapore Prime Minister Lee Hsien Loong was adamant that it was.
"I don't see our legislation being in any way restrictive of free speech. There are always rules around what you're allowed to do in terms of freedom of speech, because no free speech is absolute,'' he said.
Fake news on social media platforms was harmful and required "an immediate response'', he said.
"We have to do this and it is a step in the right direction.''
The footage of the terrorist attack on March 15 was unrelated to Singapore's new law about fake news, he said.
"His actions in Christchurch, it was not falsehood. It was true, and you have to find ways to prevent that from being circulated.''
Singapore has expressed sympathy for the victims of the March 15 attack but has not signed up to the call nor indicated support for its principles.
Mr Lee and Singapore President Halimah Yacob hosted Ms Ardern and Associate Trade and Export Growth Minister Damien O'Connor at the presidential residence in Singapore, where Ms Ardern and Mr Lee signed the Enhanced Partnership agreement.
The centrepiece was a $57 million funding pool to boost joint research on, among other things, data science and nutrition between the two nations.
Other key features include:
• Enhanced defence co-operation and a new cyber security arrangement.
• An improved working holiday scheme.
• Visa-free access for New Zealanders to Singapore for up to 90 days.
• A suite of arts and culture agreements.
At a press conference afterwards, Ms Ardern and Mr Lee both expressed concerns about the impacts of ongoing US-China trade frictions.
Mr Lee said both New Zealand and Singapore were small, trade-reliant nations and it was important to continue demonstrating the benefits of free and open trade relationships.