LOS ANGELES (CNS) — Los Angeles Mayor Eric Garcetti attended a White House event Monday at which President Joe Biden announced new regulations to rein in "ghost guns" amid a 10-fold increase in law enforcement nationwide recovering the virtually untraceable firearms during criminal investigations.

Ghost guns, which do not have serial numbers, can be assembled by unlicensed buyers from legally purchased kits. The firearms' parts — which can be ordered online — were not required under federal law to have serial numbers or a background check to purchase.

Biden announced Monday that the U.S. Department of Justice made it illegal for a business to manufacture a ghost gun kit without a serial number. The new rule classifies ghost gun kits as "firearms" under the Gun Control Act. It also makes it illegal for a licensed gun dealer to sell the kits without conducting a background check.

The new regulation also requires dealers who come into possession of a ghost gun to add a serial number to the firearm before reselling it.

"All of a sudden, it's no longer a ghost (gun.) It has a return address that's going to help save lives, reduce crime and get criminals off the street," Biden said.

The president said he asked the attorney general to write the regulation after Congress failed to pass legislation to reform firearm laws.

The White House cited data that about 20,000 suspected ghost guns were reported to the Bureau of Alcohol, Tobacco, Firearms and Explosives after being recovered by law enforcement, a 10-fold increase from 2016.

Los Angeles has taken local steps to combat the increase in ghost guns. On Nov. 30, the City Council unanimously approved an ordinance to prohibit the possession, purchase, sale, receipt and transportation of ghost guns. Violation of the city ordinance will be punishable by a fine of up to $1,000 and/or up to six months in jail.

City Attorney Mike Feuer, who said he was invited to Biden's announcement Monday but could not attend because he is recovering from COVID-19, celebrated the new federal rule in a statement Monday.

"I applaud President Biden's actions to combat the proliferation of ghost guns. ... Unserialized, untraceable ghost guns pose a major public safety threat in neighborhoods across America," Feuer said.