Hackers linked to a Chinese intelligence agency were able to breach T-Mobile as part of a months-long campaign to spy on the mobile phone communications of high-value intelligence targets, the Journal added, without saying when the attack took place.

“T-Mobile is closely monitoring this industry-wide attack,” a company spokesman told Reuters in an email.

“At this time, T-Mobile systems and data have not been impacted in any significant way, and we have no evidence of impacts to customer information.”

It was unclear what information, if any, was taken about T-Mobile customers’ calls and communications records, according to the WSJ report.

On Wednesday, the Federal Bureau of Investigation (FBI) and the US cyber watchdog agency CISA said China-linked hackers have intercepted surveillance data intended for American law enforcement agencies after breaking into an unspecified number of telecom companies.

Earlier in October, the Journal reported that Chinese hackers accessed the networks of US broadband providers, including Verizon Communications, AT&T and Lumen Technologies, and obtained information from systems the federal government uses for court-authorised wiretapping.

Beijing has previously denied claims by the US government and others that it has used hackers to break into foreign computer systems.