( CNN ) The FBI is investigating a possible ISIS-inspired terrorist threat in the United States , law enforcement officials said Saturday . The investigation originated from intercepted chatter and other intelligence information that led officials to believe a possible plot could be in the works , the officials said . No arrests have been made . It 's not clear whether the threat is real or aspirational . The exact nature of the threat could n't be learned . One official said it focused on parts of California where officials stepped up security , a U.S. official said . The Transportation Security Administration alerted local law enforcement agencies that are responsible for external security around airports , but officials said the possible threat is not necessarily aviation-related . Some cities around the United States have increased their security as a precaution . A Department of Homeland Security spokesperson declined Saturday to talk about specifics , but spoke about security measures in general . `` Over the last few months , we have made a number of security adjustments , including enhanced screening at select overseas airports and increasing random searches of passengers and carry-on luggage on flights inbound to the U.S. , reflecting an evolving threat picture , '' the spokesman said . He said the DHS added layers of security to the Electronic System for Travel Authorization . ETSA is an online application system to screen travelers before they are allow to board an airplane or ship bound for the United States . In February , a more visible law enforcement presence was put in place at federal facilities , he said . `` The department has conducted significant outreach efforts ... with state and local law enforcement partners regarding these trends and engaging in a series of meetings and events with local community leaders across the country to counter violent extremism , '' he said .
Officials say the investigation originated from intercepted chatter . Possible threat focused on parts of U.S. , one says .