The declaration follows recent news of an incident where Salt Typhoon, an infamous Chinese state-sponsored threat actor, breached T-Mobile's network in a cyber-espionage campaign on behalf of the country’s government.

T-Mobile has severed its connection to the unnamed wireline provider, which it suspects may still be compromised.

T-Mobile says the Chinese "Salt Typhoon" hackers who recently compromised its systems as part of a series of telecom breaches first hacked into some of its routers to explore ways to navigate laterally through the network.

Salt Typhoon deployed various methods to break into telecommunications firms that went far beyond a singular run-of-the-mill credential-stealing attempt, according to a person familiar.

T-Mobile, one of America's largest wireless carriers, has confirmed it was compromised in a recent wave of sophisticated cyberattacks targeting U.S. telecom companies.