An electronic message from "overseas" described as a credible bomb threat has led Los Angeles to shut down its entire school system, according to multiple news reports. Meanwhile, New York City officials also reported receiving the same "generic" threat, but determined it was "not a credible threat," police officials said Tuesday.

In LA, school officials would not elaborate on the nature of the threat, except to say it was made against many students at multiple schools. With 640,000 students at over 1,000 schools, LA's school system is the second largest in the nation. The LAPD and FBI are investigating the threat.

Reuters reports that the threat has been tracked to an IP address in Frankfurt, Germany. However, IP addresses are easy to fabricate using a Tor browser, so it's unclear the person who made the threat is actually in Frankfurt.

Meanwhile, the nation's largest school system remains open. New York Police Commissioner Bill Bratton told reporters that the city had received a similar threat, but determined it was a hoax. He also dismissed LA's response to the overseas message as an overreaction. Still, the NYPD says it is working closely with the FBI, the LAPD, and the Joint Terrorism Task Force to determine the origins of the threat.

LA officials are on edge after a rampage by a married couple with alleged terrorist sympathies left 14 people dead and 22 injured in San Bernardino earlier this month. There have been numerous reports of bomb threats in the weeks since the massacre, according to The New York Times.