The U.S. Secret Service has uncovered and dismantled a massive illegal electronic device network capable of crippling New York City’s cell towers and even jamming 911 calls, officials revealed Tuesday.

The discovery comes just days before world leaders are set to arrive in Manhattan for the United Nations General Assembly.

Investigators seized more than 300 co-located SIM servers and 100,000 SIM cards at multiple sites within 35 miles of the UN headquarters.

Officials have not released details on potential suspects, but they emphasized that the plot posed a serious threat to the city’s communications infrastructure.The investigation is ongoing.