US President Donald Trump has signed an order to ban bump-stock devices, which were used by a gunman who killed 58 Las Vegas concert-goers last year.
Such devices enable a rifle to shoot hundreds of rounds a minute.
Speaking at the White House, Mr Trump said he had directed the justice department to propose a law to make the accessories illegal.
The gun control debate took on a new urgency after 17 people were killed at a school in Florida last week.
Students and parents affected by the massacre at Marjory Stoneman Douglas High School are planning a demonstration in the state capital of Tallahassee on Wednesday.