Donald Trump has banned a gun device which allows semi-automatic weapons to fire like machine guns, after they were used in the Las Vegas shooting.
A ban on bump stocks was signed on Tuesday, and owners will have until late March to turn them in or destroy them.
The ban will be in force 90 days after it is published in the federal register which is expected to happen on Friday.
The attachment allows semi-automatic weapons to fire as a machine gun would, and became a focal point of the gun control debate when they were used by Stephen Paddock to open fire on a music festival in Nevada in October last year.
It became the worst mass shooting in US history.
The ban comes as Mr Trump met with a school safety panel, set up in the wake of the massacre in Parkland, Florida, which recommended arming teachers and using veterans as guards.
The Federal Commission on School Safety panel rejected calls to increase the minimum age to purchase a gun, arguing that most school gunman get their weapons from friends or family.
It suggested arming staff, saying schools in rural districts would particularly benefit.
Bump stock owners will be required to destroy them or turn them in to the Bureau of Alcohol, Tobacco, Firearms and Explosives (ATF).
The devices are not traceable, so it's impossible for authorities to be completely sure about how many are owned in America. The bureau estimates between 28,000 and 520,000 have been sold since 2010.
Sarah Huckabee Sanders said the move was Mr Trump "once again fulfilling a promise he made to the American people".
The president promised a ban in March saying the device turns "legal weapons into illegal machines".
In 2010 the ATF ruled bump stocks did not amount to machine guns and could not be regulated unless Congress changed existing firearms laws or passed a new one.
In the aftermath of the Las Vegas shooting, Congress sought to ban bump stocks, but no new legislation was passed.
At least 10 states have sought to introduce their own restrictions since October last year.
Gun Owners of America said it would file a lawsuit against the Justice Department and the ATF to protect gun owners from "unconstitutional regulation".
Erich Pratt, executive director, said: "These regulations implicate Second Amendment rights, and courts should be highly suspect when an agency changes its 'interpretation' of a statute in order to impair the exercise of enumerated constitutional rights."
The Justice Department pledged to fight any legal challenge.
The National Rifle Association (NRA) called the decision "disappointing" and called for an amnesty for bump stock owners.
More from US
They added: "We are disappointed that this final rule fails to address the thousands of law-abiding Americans who relied on prior ATF determinations when lawfully acquiring these devices."
In April, Slide Fire Solutions, the largest manufacturer of bump stocks, announced it would stop taking orders and shut down its website. Their remaining stock was being sold by Texan company RW Arms.
[contf] [contfnew] 
Sky News
[contfnewc] [contfnewc]
