Trump announced his support for the ban nearly a week after 14 students and three teachers were killed at a high school in Florida by a former student.
"Just a few moments ago, I signed a memorandum directing the attorney general to propose regulations to ban all devices that turn legal weapons into machine guns," the president said.
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Speaking at a White House event to honour a dozen Americans for heroism, Trump said he expected these "critical regulations" to be finalized "very soon."
A spokeswoman for the Department of Justice said it had "acted quickly to move through the rule making process. We look forward to the results of that process as soon as it is duly completed."
Calls to ban bump stocks have been mounting since Vegas shooter Stephen Paddock used them to kill 58 concert goers in October 2017, in the deadliest mass shooting in recent US history.
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A ban on bump stocks is one of the rare gun control moves which has also won the support of the powerful National Rifle Association gun lobby.
"We cannot merely take actions that make us feel like we are making a difference," Trump said. "We must actually make a difference.
"We must move past clichés and tired debates and focus on evidence-based solutions and security measures that actually work," he said.
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