Trump moves to ban 'bump stocks' 4 months after Las Vegas shooting

— -- President Donald Trump announced Tuesday he has signed a memorandum directing Attorney General Jeff Sessions to propose new regulations that would ban devices that can effectively turn legal weapons into machine guns.

The news comes four months after the Las Vegas concert mass shooting, in which the gunman was found to have used 'bump stocks' that significantly increased the rate of fire for the multiple assault weapons he used from his perch on an upper floor of the Mandalay Bay hotel.

"I expect that these critical regulations will be finalized, Jeff, very soon," Trump said during a ceremony in the White House for Medal of Valor recipients. "The key in all of these efforts, as I said the day after shooting, is that we must not take actions that make us feel like we are making a difference - we must take actions that actually make a difference."

Sen. Dianne Feinstein, the ranking Democrat on the Senate Judiciary Committee, released a statement underscoring her contention that the Bureau of Alcohol, Tobacco, Firearms and Explosives does not have authority to ban bump stocks, and that "legislation is the only answer."

"The agency made this clear in a 2013 letter to Congress, writing that ‘stocks of this type are not subject to the provisions of federal firearms statutes,’" Feinstein said.

“If ATF tries to ban these devices after admitting repeatedly that it lacks the authority to do so, that process could be tied up in court for years," Feinstein said, "and that would mean bump stocks would continue to be sold."

"If you want these devices off the street," Feinstein told Trump, "call congressional Republicans and tell them to stop blocking our bill.”

Trump's announcement comes as the administration faces new pressure over accusations of inaction in the wake of multiple deadly shootings, most recently last week's school shooting in Parkland, Florida.

President Trump will host individuals impacted by some of the country's worst school shootings for a listening session at the White House on Wednesday, according to press secretary Sarah Sanders.

Sanders told reporters Tuesday that community members and victims from last week's Parkland, Fla. school shooting, as well as victims from the Columbine and Sandy Hook shootings, have been invited to meet at the White House.

Sanders said the listening session would focus on a "wide range of issues."

"You have a number of people that have unfortunately been through horrific tragedy like the one we saw in Parkland, Florida, last week as well as some that hope they never have to go through that," Sanders said. "This is a listening session to see what can be done better, what the actual concerns of the students are, what they would like to see."

After the shooting in Parkland, a number of students have called for marches across the country to promote new gun restrictions. The White House has so far only stated support for a bill that would seek to improve the national background check system.

Sanders did not answer definitively, however, when asked whether the president would oppose reinstating a ban on assault weapons.

“We haven't closed the door on any front,” Sanders said. “That's what the next several days and weeks will be, to have conversations and see what this process looks like.”

The briefing is Sanders' first in a week, after the White House cancelled a Valentine's Day briefing, citing the school shooting in Parkland, Florida.

ABC News' Ali Rogin contributed to this report.