US president Donald Trump has directed the justice department to move to ban devices like the rapid-fire bump stocks used in last year's Las Vegas massacre.
The move comes as a Florida community grieving over the deaths of 17 people in a high school shooting last week demanded tougher gun control.
Mr Trump said: "We must do more to protect our children," adding that his administration was working hard to respond to the shooting at Marjory Stoneman Douglas High School in Parkland.
Former pupil Nikolas Cruz (19) has been charged with 17 counts of premeditated murder over the shootings on Valentine's Day.
After past mass killings yielded little action on tighter gun controls, the White House is trying to demonstrate that it is taking the issue seriously.
The president, a strong and vocal supporter of gun rights, has not endorsed more robust changes sought by gun control activists. But the White House cast the president in recent days as having been swayed by the school shooting in Florida and willing to listen to proposals.
In a tweet on Tuesday night, Mr Trump indicated he wants to strengthen the background check system, but offered no specifics.
He said: "Whether we are Republican or Democrat, we must now focus on strengthening Background Checks!"
When asked if Mr Trump was open to reinstating a ban on assault-type weapons, White House spokeswoman Sarah Huckabee Sanders said officials "haven't closed the door on any front". She also said that the idea of raising the age limit to buy an AR-15 rifle was "on the table for us to discuss".
Later on Wednesday, Mr Trump will host parents, teachers and students at the White House for a "listening session" that will include people affected by mass shootings in Parkland, Columbine, Colorado and Newtown, Connecticut.
Senator Chris Murphy, a Connecticut Democrat and leading advocate for tighter gun controls, said Mr Trump's directive suggested the president was aware of fresh energy on the issue and called it a sign that "for the first time" politicians are "scared of the political consequences of inaction on guns".
A bipartisan legislative effort to ban bump stocks last year fizzled out. The Bureau of Alcohol, Tobacco, Firearms and Explosives (ATF) announced in December that it was reviewing whether weapons that use bump stocks should be considered illegal machine guns under federal law.
The US justice department had not made any announcement regarding its review when Mr Trump signed a memorandum directing the agency to complete the review as soon as possible and propose a rule "banning all devices that turn legal weapons into machine guns".
Gun control advocates want to close loopholes that permit loose private sales on the internet and at gun shows, as well as banning assault-type weapons and passing laws to enable family members, guardians or police to ask judges to strip gun rights temporarily from people who show warning signs of violence.
The Parkland shooting also has prompted the Republican-controlled Florida legislature to take a fresh look at gun control legislation, although so far Republican leaders are refusing to endorse calls to ban assault rifles.
