The US Secret Service has dismantled a network of electronic devices near the UN in New York ahead of a speech by the United States president.

The service revealed it had identified an "imminent threat" to Donald Trump. It comes as global leaders gather in the American city for the UN General Assembly. The network of sim cards and servers could have jammed the telephone network and prevented 911 calls from being made or answered.

The Secret Service - which is responsible for protecting Trump and other top officials - discovered some 300 SIM servers and 100,000 SIM cards scattered across multiple sites in the New York tristate area, it has said.

The extensive network was capable of shutting down mobile networks and of protecting communication between hostile actors, it said.

According to the agency's director, Sean Curran, the "potential for disruption to our country’s telecommunications posed by this network of devices cannot be overstated".

Officials warned the devices had the capability of carrying out a wide-range of telecommunications attacks which could have included spamming networks with up to 30 million text messages a minute, which would have had “catastrophic” consequences for the city, authorities said.

Matt McCool, the special agent in charge of the Secret Service’s New York field office, told reporters: “It can take down cell towers, so then no longer can people communicate, right? …. You can’t text message, you can’t use your cell phone.

"And if you coupled that with some sort of other event associated with UN General Assembly, you know, use your imagination there, it could be catastrophic to the city."

Mr McCool added that the hidden network was found as part of a sweeping Secret Service probe that kicked off in the spring following telecommunications-related threats targeting senior US government officials, according to investigators.

When agents ultimately raided the locations, they uncovered rows of servers and shelves stacked with SIM cards, including more than 100,000 that had already been activated, as well as a large number still waiting to be deployed, he added.

Mr McCool said forensic analysis is still in its early stages, he added: "We need to do forensics on 100,000 cell phones, essentially all the phone calls, all the text messages, anything to do with communications, see where those numbers end up."

There was no reporting of a specific threat to the General Assembly, but the Secret Service said it moved quickly to dismantle the network, as the respective devices were located within 35 miles of the global summit.