The FBI and CISA previously said they were investigating breaches by a China-backed hacking group inside several telecommunications providers, but had not said whether any data was stolen or whether the hackers accessed the systems used to fulfill legal wiretap requests.

The disclosure is the latest sign that the Chinese burrowed deep inside U.S. communications networks in a far-reaching espionage campaign.

CISA and the FBI have confirmed that Chinese hackers compromised the networks of telecommunications companies to spy on specific targets.

U.S. agencies disclosed that some government officials saw their communications compromised in connection with a major telecom hacking operation tied to the Chinese government.

WASHINGTON (Reuters) -China-linked hackers have intercepted surveillance data intended for American law enforcement agencies after breaking in to an unspecified number of telecom companies, U.S. authorities said on Wednesday.