Iran may have issued an operational signal to activate “sleeper assets” worldwide as tensions with the United States and Israel intensify, according to a report citing a federal alert circulated to U.S. law enforcement agencies.

The alert said U.S. intelligence officials intercepted encrypted communications believed to have originated in Iran shortly after the reported death of Supreme Leader Ali Khamenei in a joint U.S.-Israeli strike on February 28, ABC News reported.

Authorities warned the transmission could represent “an operational trigger” designed to activate or issue instructions to prepositioned sleeper operatives outside the country.

The alert stated that the message was “likely of Iranian origin,” though investigators have not yet been able to determine the precise content of the communications.

Officials said the sudden emergence of a new broadcast signal with characteristics suggesting international retransmission has prompted heightened vigilance among security agencies.

“While the exact contents of these transmissions cannot currently be determined, the sudden appearance of a new station with international rebroadcast characteristics warrants heightened situational awareness,” the alert said.