A US judge has blocked the planned release of 3-D printed gun blueprints hours before they were set to hit the internet.
District Judge Robert Lasnik in Seattle sided with states that sued to halt the publication of designs to make weapons that security screening may not detect.
Lasnik said the blueprints' publication could cause irreparable harm to US citizens.
The decision blocked a settlement President Donald Trump's administration had reached with Texas company Defense Distributed, which initially said it planned to put files online on Wednesday.
Gun control proponents are concerned the weapons made from 3-D printers are untraceable, undetectable "ghost" firearms that pose a threat to global security.
But gun rights groups say the technology is expensive, the guns are unreliable and the threat is being overblown.
Josh Blackman, a lawyer for Defense Distributed, said during Tuesday's hearing that blueprints had already been uploaded to the firm's website on Friday.
The publication of those files is now illegal under federal law, Lasnik said.
"There are 3-D printers in public colleges and public spaces and there is the likelihood of potential irreparable harm," Lasnik said.
Defense Distributed and its founder Cody Wilson, a self-declared anarchist, argued that access to the online blueprints is guaranteed under the US constitution.
Eight states and the District of Columbia on Monday filed a lawsuit against the federal government, saying online blueprints would allow criminals easy access to weapons.
Earlier on Tuesday, Trump raised concerns about the sale of plastic guns made with 3-D printers and said on Twitter he had talked with the powerful National Rifle Association lobbying group about the weapons.
"I am looking into 3-D Plastic Guns being sold to the public," he said. "Already spoke to NRA, doesn't seem to make much sense."
The NRA followed suit.
"Regardless of what a person may be able to publish on the Internet, undetectable plastic guns have been illegal for 30 years," Chris Cox, executive director of the NRA's Institute for Legislative Action, said in a statement.