The White House said it supports the goals of the call to action in the name of Christchurch, but would not sign on because of freedom of speech concerns.
The United States says it supports an international effort to find ways to stop social media from spreading hate — but won't take part in it.
In a statement issued Wednesday, the White House praised the call to action in the name of Christchurch being spearheaded by New Zealand Prime Minister Jacinda Ardern and French President Emmanuel Macron.
"The United States stands with the international community in condemning terrorist and violent extremist content online in the strongest terms," the White House said, but added that it is "not currently in a position to join the endorsement."
That makes the U.S. an outlier. Allies including the United Kingdom, Japan, Australia, Italy, India, Germany and Spain are all listed as signing on to the effort. Numerous technology giants are involved as well, including Amazon, Facebook, Google, Twitter and YouTube.
In its statement, the White House suggested that First Amendment concerns were stopping the Trump administration from joining in the agreement.
"We continue to be proactive in our efforts to counter terrorist content online while also continuing to respect freedom of expression and freedom of the press," the statement said.
In an op-ed in The New York Times this past weekend, Ardern said the "Christchurch Call" would be a voluntary framework that "commits signatories to counter the drivers of terrorism and put in place specific measures to prevent the uploading of terrorist content."
It's named after the New Zealand city where a white supremacist attacked two mosques in a shooting spree that left 51 people dead. Parts of the March 15 attacks were livestreamed on Facebook.
The attacker's digital footprint along with his own claims about how the internet shaped his views led to renewed calls for social media platforms to do more to combat hate speech as well as foreign governments that said they were prepared to take matters into their own hands.
Ahead of the meeting with world leaders and other tech companies in Paris for a "Tech for Good" summit Wednesday, Facebook announced that it would be implementing new rules around the company's livestream tool in an effort to limit its use to "cause harm or spread hate."
In a rare joint statement, Facebook, Twitter, Google, Amazon and Microsoft said: "The terrorist attacks in Christchurch, New Zealand, in March were a horrifying tragedy. And so it is right that we come together, resolute in our commitment to ensure we are doing all we can to fight the hatred and extremism that lead to terrorist violence."