Iran may be activating sleeper cells outside the country, alert says

The U.S. has intercepted encrypted communications believed to have originated in Iran that may serve as "an operational trigger" for "sleeper assets" outside the country, according to a federal government alert sent to law enforcement agencies.

The alert, reviewed by ABC News, cites "preliminary signals analysis" of a transmission "likely of Iranian origin" that was relayed across multiple countries shortly after the death of Ayatollah Ali Khamenei. Khamenei, the supreme leader of Iran, was killed in a U.S.-Israeli attack on Feb. 28.