The US government has revealed a “broad and significant” cyber espionage campaign targeting the country’s commercial telecommunications infrastructure by hackers linked to China.

In a statement, the FBI and the Cybersecurity and Infrastructure Security Agency, which led the investigation, said China-affiliated actors had “compromised networks at multiple telecommunications companies.”

The breaches allowed data from customer call logs to be stolen, private communications of a limited number of people involved in government or political activities were compromised, and some information subject to US law enforcement requests was copied.

“We expect our understanding of these compromises to grow as the investigation continues,” the statement said.

Other potential victims were alerted and the two agencies said they were working to strengthen cyber defenses in the commercial communications sector.

The affected companies were not named in the statement, however, news outlets reported a month ago that a China-linked group called Salt Typhoon attacked networks operated by AT&T, Verizon and Lumen.

The hacks targeted the phones of presidential candidates Donald Trump and Kamala Harris in the run-up in the US elections.