Fears have grown in the US that Tehran could activate “sleeper cells” or carry out unconventional retaliatory attacks on American soil as Washington and Tel Aviv continue their war against Iran.
President Donald Trump warned on Wednesday that his administration knows where the Iranian sleeper cells are and is monitoring all of their members. The statement appeared aimed both at reassuring the public and sending a warning to Iran.
Still, the tone contrasts with more cautious assessments from US security agencies, which say the threat remains potential rather than imminent or specific.
Security agencies on alert
Trump’s remarks followed earlier comments in which he said the situation was “under control” and that authorities were “watching everyone” of the suspected sleeper cells.
While the president sought to link the issue to immigration, security agencies have adopted a more measured approach. A US intelligence assessment issued after the killing of Iran’s Supreme Leader Ali Khamenei warned that Iran and its proxies could resort to selective attacks inside the United States, though large-scale assaults are considered less likely.
Officials see a higher probability of cyberattacks or smaller operations carried out by limited networks or sympathetic individuals.
The Department of Homeland Security has similarly assessed that Iran and its proxies could pose a threat through targeted attacks inside the United States.
Against that backdrop, Kash Patel, director of the Federal Bureau of Investigation, announced on Feb. 28 that the bureau had placed its counterterrorism and intelligence teams on “maximum alert.”
The move included mobilizing additional security resources and emphasizing that the FBI’s Joint Terrorism Task Forces nationwide are working around the clock to detect and disrupt potential threats. Such measures typically involve heightened surveillance of high-priority suspects, expanded use of confidential sources, reviews of technical intelligence tools and closer coordination between federal and local authorities.
Drone concerns in California
One development that drew attention in recent days was the disclosure of a confidential FBI bulletin circulated through the Los Angeles Joint Regional Intelligence Center before the outbreak of the war.
The notice warned that Iran might attempt to retaliate for US attacks by launching drones from ships at sea targeting California.
According to a security bulletin reviewed by Reuters, the FBI distributed the warning last month to law enforcement agencies, citing information collected in late February suggesting Iran could plan a surprise drone attack launched from a vessel offshore if Washington carried out strikes against it.
The bulletin, however, contained no specific information on timing or targets and described the scenario more as a potential ambition than a confirmed operational plan. It also said no further details were available regarding how such an attack might be carried out or who might be involved.
Details of the bulletin emerged publicly as the war, which began with US and Israeli strikes on Iran on Feb. 28, entered its twelfth day.
Vigilance but no imminent threat
California authorities sought to balance caution with reassurance. Governor Gavin Newsom said the state was aware of the warning and was coordinating closely with federal and local agencies while preparing for worst-case scenarios. He stressed that no credible or imminent threats had been identified.
Los Angeles Mayor Karen Bass and San Francisco Mayor Daniel Lurie delivered similar messages, saying no specific threat had been detected but that coordination with federal authorities was ongoing.
Local police departments across the state said they had been informed of a higher risk environment and urged residents to report suspicious activity.
Past incidents
Previous cases have heightened US concerns. In July 2021, the Justice Department revealed a plot linked to an Iranian intelligence network to kidnap journalist and activist Masih Alinejad from New York and forcibly take her to Iran.
In March 2025, a federal court convicted two leaders of an Eastern European organized crime network in a murder-for-hire scheme targeting Alinejad on behalf of actors linked to Iran’s Revolutionary Guard Corps.
They were sentenced in October that year to 25 years in prison each. Another defendant involved in surveilling Alinejad and planning her killing in New York was sentenced in January 2026 to 15 years in prison.
