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The cache, made up of more than 300 SIM servers packed with over 100,000 SIM cards and clustered within 35 miles of the United Nations, represents one of the most sweeping communications threats uncovered on U.S. soil. Investigators warn the system could have blacked out cellular service in a city that relies on it not only for daily life but for emergency response and counterterrorism.

Forensic analysis is still in its early stages, but agents believe nation-state actors " perpetrators from particular countries " used the system to send encrypted messages to organized crime groups, cartels and terrorist organizations, McCool said. Authorities have not disclosed details on the specific government or criminal groups tied to the network at this point.