American counterterrorism agencies are intensifying surveillance of suspected sleeper cells within the United States following a joint United States and Israel military strike on Iran that killed Iran's Supreme Leader and other senior officials. Although authorities say there are no specific or credible threats at this time, federal and local law enforcement have increased security in major cities as a precaution against possible retaliation.

Security experts warn that Iranian-backed groups such as Hezbollah and Hamas have maintained networks and sympathizers inside the United States for decades. Former Federal Bureau of Investigation officials caution that these organizations, along with lone actors inspired by overseas events, could view the recent military action as motivation to carry out attacks.

The Federal Bureau of Investigation and the Department of Homeland Security have placed counterterrorism and intelligence teams on high alert, coordinating closely to monitor evolving threats. While officials emphasize that heightened vigilance is routine during periods of international conflict, they acknowledge that the domestic threat environment could shift quickly as tensions with Iran continue.