Growing power of Chinese cyber facilities is posing a great concern for the United States, the top intelligence official told a Senate panel.

"The Chinese have made a substantial investment in this area, they have a very large organization devoted to it and they're pretty aggressive," Director of National Intelligence James Clapper told the Senate Armed Services Committee.

"This is just another way in which they glean information about us and collect on us for technology purposes, so it's a very formidable concern," he said.

While Clapper did not detail what exactly China has at its deposal in his written testimony, the intelligence chief said that in 2010 there was a "dramatic increase in malicious cyber-activity targeting U.S. computers and networks." The passage did not specifically mention China.

Clapper also cited an April 8, 2010, incident in which state-owned China Telecom advertised erroneous network routes that instructed "massive volumes" of U.S. and other foreign Internet traffic to go through Chinese servers for 17 minutes.

"This incident affected traffic to and from U.S. government and military sites, including sites for the Senate, the Army, the Navy, the Marine corps, the air force, and the office of the Secretary of Defense, as well as a number of Fortune 500 firms," he said.