Obama's former DHS secretary sounds alarm on Iranian sleeper cells, calls it concern of 'highest magnitude'

The former Homeland Security Secretary under President Barack Obama is warning that the threat of terror sleeper cells on American soil is a major concern for law enforcement.

"That's not necessarily all of them," he said. "My educated speculation is that law enforcement has been tracking these individuals for a while in this country to follow leads, to see who they are in contact with." 

"We don't know who they are, where they came from, why they're here, but they got away," said Homan on Tuesday, going on to call it the "biggest national security vulnerability" the country has seen. 

Besides Iranian attacks, Johnson noted that those with extremist ties could act independently in response to the growing tensions in the Middle East.

"Sleepers don't necessarily follow the direction from their sponsors," he said. "Somebody who's here in the United States who has links to the IRGC, to Hezbollah, may decide to take matters into their own hands."

Instead, he urged the public to remain vigilant and report any suspicious activity to the authorities. 

"'If you see something, say something' is still a valid public safety tool," he said. "It does make a difference."