Shortly after the president's comments, the Justice Department announced that it had started the process to amend federal firearms regulations to define bump stocks as machine-guns.
The devices were used by Las Vegas shooter Stephen Paddock on a dozen rifles he deployed to kill 58 people and wound 500 at an open concert previous year, the deadliest mass shooting in recent U.S. history.
The Justice Department said the attachments will be banned beginning in late March under a law that prohibits machine guns.
Justice Department officials say they don't know exactly how many bump stocks are privately owned, but they estimate the number in the tens of thousands.
"We are faithfully following President Trump's leadership by making clear that bump stocks, which turn semi-automatics into machine guns, are illegal, and we will continue to take illegal guns off of our streets", Whitaker said in a statement.
Instead, a regulation was signed by Matthew Whitaker, the acting attorney general, on Tuesday.
Pro-gun advocates have said they are prepared to fight the rule in court. The department followed up by proposing a federal rule change that would reclassify bump stocks so they fell under the definition of a "machine gun", as it's now doing. After that, it will be illegal to possess bump stocks.
Following the shooting Mr Trump said he would ban the devices.
Following the Las Vegas shooting the devices became a focal point in the national gun control debate. The most powerful United States gun rights organization said that the amendment "fails to address thousands of law-abiding Americans" who relied on previous ATF interpretations in purchasing bump stocks.
Administration officials said that the devices are not extremely common, but there are probably tens of thousands nationwide, United States media reported.
The Bureau of Alcohol, Tobacco, Firearms and Explosives (ATF) had previously ruled that bump stocks did not qualify as machine guns and thus would not be regulated.
The Trump administration is banning bump stocks, the firearm attachment that allows a semi-automatic weapon to shoot nearly as fast as a machine gun. ATF received about 186,000 comments on the proposal.
The websites for the most well-known bump stock manufacturers, Bumpfire System and Slide Fire, displayed notifications on Tuesday that they had already ceased direct sales of the devices. The gunman reportedly used bump stocks on his weapons, resulting in the death of 58 people.