U.S. investigators believe hackers affiliated with the Chinese government are responsible for a cyber intrusion on an internal Federal Bureau of Investigation computer network that holds information related to some domestic surveillance orders, the Wall Street Journal reported on Friday.

The scope and severity of the intrusion are not known, and the investigation is in its early stages, the report said, citing people familiar with the matter.

The FBI declined to comment. The Chinese embassy in Washington did not immediately respond to Reuters’ request for comment.

What to Know

The FBI began investigating abnormal log activity in the targeted system on its network February 17, according to a copy of a notification sent by the FBI to Congress this week reviewed by Reuters.

Hackers targeted an unclassified system that contains information about and related to the communications of people under FBI investigation, according to the notification.

The FBI described the hackers’ techniques as “sophisticated,” and said remediation and forensic investigations were ongoing.

Politico reported that the White House, National Security Agency, Department of Homeland Security’s Cybersecurity and Infrastructure Security Agency and the FBI were collaborating on an investigation into the matter.

A White House official told Reuters it “regularly convenes meetings to discuss any cyber threat to the U.S.,” but that it would not discuss the details of any particular incident or particular meetings.

CISA referred questions to the FBI, which declined to comment. The NSA did not respond to a request for comment.

(Reporting by Chris Thomas in Mexico City; Additional reporting by AJ Vicens in Detroit and Jana Winter in Washington; Editing by Mark Porter and Edward Tobin)