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.
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.
What did Trump say?
At an event on Tuesday recognising the bravery of law enforcement, Mr Trump said he had directed Attorney General Jeff Sessions to finalise new guidelines to declare bump stocks illegal “very soon”.
“The key in all of these efforts, as I said in my remarks the day after the shooting, is that we cannot merely take actions that make us feel like we are making a difference, we must actually make a difference,” he said.
“We must move past clichés and tired debates, and focus on evidence-based solutions and security measures that actually work and that make it easier for men and women of law enforcement to protect our children and protect our safety.”
What are bump stocks?
The accessories can make semi-automatic rifles fire as rapidly as machine guns.
They can be bought for as little as $100 (£70) without the need for a criminal background check. More than 500 people were also injured in that attack, considered America’s worst ever mass-shooting by a lone gunman.
Audio analysis found the attacker, Stephen Paddock, had been able to fire 90 bullets within 10 seconds from his room in the Mandalay Bay Resort and Casino.
Both Democrats and Republicans agreed in the nationwide wave of horror following the Las Vegas attack that the sale of bump stocks should be outlawed.
The device was used by a 64-year-old gambler who rained bullets on a crowd at an outdoor country music festival on the Las Vegas Strip in October last year.
But a bill introduced to ban bump stocks, trigger cranks and other devices that can speed up a semi-automatic rifle’s rate of fire has since stalled.
In December, the Bureau of Alcohol, Tobacco, Firearms and Explosives began considering a regulation for bump stocks, opening a process that drew more than 35,000 public comments.
Proposals to ban bump stocks have been put forward with mixed results at state level, including in South Carolina, Illinois, Washington and Colorado.
Previous efforts to introduce gun control measures in the wake of mass shootings in recent years have gone nowhere in the US Congress.
Might Trump consider any other gun control?
On Tuesday, the White House signalled it was open to an age limit for people buying AR-15-type assault rifles, like the one used in last week’s deadly school shooting in Parkland, Florida.
“I think that’s certainly something that’s on the table for us to discuss and that we expect to come up over the next couple of weeks,” said White House spokeswoman Sarah Sanders, when asked about a possible age requirement. The age limit in most US states for buying an AR-15 is 18.
Over the weekend, Mr Trump said he was supportive of a bipartisan bill that seeks to improve the checks in place before someone can buy a gun.
That legislation intends to patch holes in the FBI’s background check System, which processed more than 25 million gun ownership applications last year.
Failures in that database were exposed by last week’s Florida high school shooting, allegedly by a 19-year-old gunman with a history of mental health issues. Bump stocks were not used in that attack.