The US Secret Service disrupted a network of telecommunications devices that could have shut down cellular systems as leaders gather for the United Nations (UN) General Assembly in New York City.

The agency said on Tuesday that last month it found more than 300 SIM servers and 100,000 SIM cards that could have been used for telecom attacks within the area encompassing parts of New York, New Jersey and Connecticut.

"This network had the power to disable cell phone towers and essentially shut down the cellular network in New York City," said special agent in charge Matt McCool.

The devices were discovered within 35 miles (56km) of the UN, where leaders are meeting this week.

McCool said the "well-organised and well-funded" scheme involved "nation-state threat actors and individuals that are known to federal law enforcement".

The unidentified nation-state actors were sending encrypted messages to organised crime groups, cartels and terrorist organisations, he added.

The equipment was capable of texting the entire population of the US within 12 minutes, officials say. It could also have disabled mobile phone towers and launched distributed denial of service attacks that might have blocked emergency dispatch communications.

The devices were seized from SIM farms at abandoned apartment buildings across more than five sites. Officials did not specify the locations.

The discovery followed an investigation into anonymous "telephonic threats" directed at three US government officials this spring, unnamed officials told the New York Times.

One of the officials works in the Secret Service, and the other two work at the White House, according to the newspaper.

Investigators also told CBS News they found 80g of cocaine, illegal firearms, computers and phones.

More than 100 world leaders and delegations have gathered in Midtown Manhattan for the 80th anniversary of the UN General Assembly in New York.