A senior U.S. intelligence official said on Tuesday that Chinese cyber activity in the United States had risen in recent months, targeting critical infrastructure in what may be attempts to lay the groundwork for future disruptive attacks.

"You worry they are prepositioning against critical infrastructure and trying to be able to do the types of disruptive operations that would be the most concern," National Security Agency official Rob Joyce said at a Wall Street Journal cybersecurity conference.

Joyce, a former White House cyber adviser for President Donald Trump, did not elaborate. A spokeswoman for the NSA said Joyce was referring to digital attacks against the U.S. energy, financial, transportation and healthcare sectors.

The comments are notable because U.S. complaints about Chinese hacking have to date focused on espionage and intellectual property theft, not efforts to disrupt critical infrastructure.

China has repeatedly denied U.S. allegations it conducts cyber attacks.

Joyce's remarks coincide with U.S. prosecutors preparing to unveil as early as this week a new round of criminal hacking charges against Chinese nationals. They are expected to charge that Chinese hackers were involved in a cyber espionage operation known as "Cloudhopper" targeting technology service providers and their customers, according to people familiar with the matter.

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The U.S. Congress is looking into the allegations of increased Chinese hacking activity.

Senior officials from the Department of Homeland Security and Justice Department are scheduled to testify Wednesday morning at a Senate Judiciary Committee hearing on "China's Non-Traditional Espionage Against the United States: The Threat and Potential Policy Responses." (VOA)