The "messaged" threat was received electronically and mentioned backpacks and other packages, Cortines said at a morning news conference.
"It was to students at schools," he added, characterizing the threat as "rare."
LAUSD is the second largest school district in the country, serving more than 640,000 students between kindergarten and 12th grade, according to its website. There are more than 900 schools and 187 public charter schools in the district.
Parents with questions were urged to call 213-241-2064, according to LAPD.