US President Joe Biden issued an executive order on Tuesday that reinforced background checks for gun buyers, in what the White House is calling the most comprehensive policy he can enact without Congress.
He signed the new measures on reducing gun violence during a visit to the scene of a January shooting in Monterey Park, California, where 11 people were killed.
"I'm here on behalf of the American people to mourn with you, pray with you, let you know you're loved and not alone," Mr Biden said.
He is invoking the limited authority of the executive branch to edge the country closer to universal firearms background checks, something he has been unable to get through Congress, although it remains popular in voter surveys.
Mr Biden maintains that legislators should move to ban all sales of assault weapons in the country and pass universal background checks, moves many Republicans have resisted.
"Let's be clear, none of this absolves Congress from the responsibility of acting," he said.
"Pass universal background checks, eliminate gun manufacturers' immunity from liability and I'm determined once again to ban assault weapons and high-capacity magazines."
Mr Biden's order directs Attorney General Merrick Garland to identify gun sellers who are not completing background checks or may be evading them intentionally.
Gun control advocates have long raised concerns about a lack of protection with firearms sold at gun shows or by online retailers.
The order charges the Federal Trade Commission with compiling a report that examines gun makers' marketing campaigns aimed at those not old enough to buy firearms.
The order also asks cabinet members to devise an organised federal response to use in communities affected by mass shootings.
That response would include mental health care and financial assistance if, say, small businesses were forced to shut down or if families lost people who provided their income, a White House fact sheet reveals.
A senior administration official said before the order was made public on Tuesday that the federal government could do more to support families and first responders after these tragedies.
Up to March 13, there have been 109 mass shootings in the US this year, according to data collected by the Gun Violence Archive. That compares to 85 by the same date last year.
Vice President Kamala Harris visited Monterey Park after the 11 people were killed by a gunman during a Lunar New Year celebration in the mainly Asian-American community. Nine were wounded.
Ms Harris called on Congress to enact “reasonable gun safety laws".
Last year, Congress passed the first nationwide gun-control legislation in 30 years, introducing measures to improve the national background-check system for buyers under 21.
It also closed the "boyfriend" loophole that allowed dating partners convicted of domestic abuse to buy guns.
Bloomberg contributed reporting
