Verizon Communications, AT&T and Lumen Technologies are among the telecoms companies whose networks were breached by the recently discovered intrusion, the Wall Street Journal reported, citing people familiar with the matter.
The hackers might have held access for months to network infrastructure used by the companies to co-operate with court-authorised US requests for communications data, the Journal said.
It said the hackers had also accessed other tranches of internet traffic.
China's foreign ministry responded on Sunday that it was not aware of the attack described in the report but said the US had "concocted a false narrative" to "frame" China in the past.
"At a time when cybersecurity has become a common challenge for all countries around the world, this erroneous approach will only hinder the efforts of the international community to jointly address the challenge through dialogue and cooperation," the ministry said in a statement to Reuters.
Beijing has previously denied claims by the US government and others that it has used hackers to break into foreign computer systems.
Verizon, AT&T and Lumen Technologies did not immediately respond to requests for comment.
The Journal said the attack was carried out by a Chinese hacking group to collect intelligence.
US investigators have dubbed it "Salt Typhoon".
Earlier this year, US law enforcement disrupted a major Chinese hacking group nicknamed "Flax Typhoon" months after confronting Beijing about sweeping cyber espionage under a campaign named "Volt Typhoon".
In its statement, China's foreign ministry said Beijing's cybersecurity agencies had found and published evidence to show Volt Typhoon was staged by "an international ransomware organisation".
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