The encrypted transmission was intercepted by the U.S. 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. The intercepted transmission was encoded and appeared to be destined for "clandestine recipients" who possess the encryption key, the kind of message intended to impart instructions to "covert operatives or sleeper assets" without the use of the internet or cellular networks.…