The hackers compromised the networks of “multiple telecommunications companies” and stole US customer call records and communications from “a limited number of individuals who are primarily involved in government or political activity,” according to a joint statement released by the FBI and the US cyber watchdog agency CISA.

The two agencies said the hackers also copied “certain information that was subject to US law enforcement requests pursuant to court orders.”

The statement gave few other details and the Cybersecurity and Infrastructure Security Agency did not immediately respond to a request for comment. The FBI declined to comment.

The announcement confirms the broad outlines of previous media reports, especially those in the Wall Street Journal, that Chinese hackers were feared to have opened a back door into the interception systems used by law enforcement to surveil Americans’ telecommunications.

That, combined with reports that Chinese hackers had targeted telephones belonging to then-presidential and vice-presidential candidates Donald Trump and JD Vance, along with other senior political figures, raised widespread concern over the security of America’s telecommunications infrastructure.

The matter is already slated for investigation by the Department of Homeland Security’s Cyber Safety Review Board, which was set up to analyse the causes and fallout of major digital security incidents.

The Chinese Embassy in Washington did not immediately return a message seeking comment. Beijing routinely denies US hacking allegations.