What Is a Sleeper Cell — Here's What You Need to Know About Encrypted Iranian Messages That Could Target the West

The encrypted message was designed to reach people who were never meant to be found.

According to a federal alert reviewed by ABC News, US intelligence intercepted a transmission 'likely of Iranian origin' relayed internationally shortly after the death of Supreme Leader Ayatollah Ali Khamenei on 28 February.

The encoded broadcast appeared destined for 'clandestine recipients' possessing the encryption key, the kind of message meant to impart instructions to 'covert operatives or sleeper assets' without using the internet or cellular networks.

That last detail matters a lot.

Old Spycraft, New Threat

The method mirrors what intelligence veterans call 'numbers stations'. These shortwave radio broadcasts date back to World War I. During the Cold War, the CIA considered such one-way voice link transmissions 'unbreakable' when operatives followed proper tradecraft. The signals bounce off the ionosphere, reach basic radios anywhere on Earth, and leave no metadata trail.

The federal alert warned that 'the sudden appearance of a new station with international rebroadcast characteristics warrants heightened situational awareness.'

Put simply: a transmission hub popped up after Khamenei died, started broadcasting across multiple countries, and US authorities don't know what the messages say.

So What Exactly Is a Sleeper Cell?

The term gets thrown around often. Here's what it actually means.

A sleeper cell consists of covert operatives embedded in a target country. They live normal lives. Hold jobs. Pay rent. They maintain no visible connection to handlers and only act when triggered by a specific signal or event.

In 2016, a man from Lebanon told the FBI after his arrest that he belonged to such a cell. According to The Jerusalem Post, when agents asked under what circumstances he might be activated, he answered plainly: 'If the United States went to war against Iran.'

That hypothetical is now a reality. US and Israeli forces have been striking Iranian targets since late February. Khamenei is dead. The conditions the operative described have arrived.

What the FBI Is Doing

FBI Director Kash Patel said he has 'instructed our counterterrorism and intelligence teams to be on high alert and mobilise all assisting security assets needed.' The bureau, he added, 'remains at the forefront of deterring attacks here at home.'

The alert itself notes there is 'no operational threat tied to a specific location.' But law enforcement agencies have been told to increase monitoring of suspicious radio-frequency activity.

Two violent incidents with potential Iranian links occurred within days of the intercept.

In Austin, Texas, a 53-year-old suspect opened fire at a bar early Sunday, killing two and wounding 14. According to Iran International, police found an Islamic Republic flag and photographs of Iranian leaders inside his apartment. He wore a sweatshirt reading 'Property of Allah' during the attack.

Hours later in Toronto, gunfire struck a boxing gym run by Iranian-Canadian dissident Salar Gholami. Bullet holes lined the front windows.

The FBI and Joint Terrorism Task Force are assisting in the Austin investigation.

Years of Disrupted Plots

None of this is new. Federal authorities say they have disrupted at least 17 Iranian plots on US soil since the 2020 killing of Qassem Soleimani, including murder-for-hire and kidnapping schemes documented in court filings.

'If ever there's going to be a Hezbollah cell or a Hamas cell act in the United States in a violent way, it's now,' Chris Swecker, a former assistant FBI director, told Fox News. 'Both organisations have had a presence in the United States since the 1980s.'

The encrypted broadcasts remain undeciphered. The infrastructure to receive and act on them may already be in place.

The message was designed to reach people who were never meant to be found. Whether it reached them is what authorities are now racing to learn.