The modification allows semi-automatic weapons to fire like automatic weapons and was used by a gunman who killed 58 Las Vegas concert-goers last year.
US President Donald Trump has called for a ban on bump stocks, a device that allows a semiautomatic rifle to fire at the rate of a machine gun.
Last week’s Florida school shooting – which killed at least 17 people, including 14 students – sparked renewed debate on gun control. Survivors of the shooting have made pleas for increased regulations.
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“If the president wants to come up to me and tell me to my face that it was a terrible tragedy and how it should never have happened and maintain telling us how nothing is going to be done about it,” survivor Emma Gonzalez said at a speech at a gun control rally on Saturday.
Trump has tweeted his support for increased background checks, saying both Republicans and Democrats should focus on the issue.
The president also signed an order calling for US Attorney General Jeff Sessions to create a ban on “bump stocks”, a modification that allows for increased shooting speed for assault-style weapons. A bump stock was used in the 2017 Las Vegas shooting that killed 58 people.
“It took until now, four months later, for president Donald Trump to take action,” Al Jazeera’s Heidi Zhou-Castro, reporting from Washington DC, said.
But gun safety advocates say it is only the bare minimum of what the government should do to prevent mass shootings.