WASHINGTON, USA: The head of a U.S. agency that helps respond to cyber attacks resigned suddenly after several high-profile attacks on government computer systems but the Department of Homeland Security declined on Monday to comment on the reason.

Randy Vickers resigned as director of the U.S. Computer Emergency Readiness Team on Friday, according to an email from Roberta Stempfley, acting assistant secretary for cyber security and communications at Homeland Security, which was sent to some employees.

The email, obtained by Reuters, did not disclose any reason for the resignation, and a Homeland Security official would only say: "we aren't commenting on personnel matters."

Vickers' resignation follows several high-profile hacker attacks against the Pentagon and public websites of the Central Intelligence Agency and U.S. Senate.

Lee Rock, who was deputy director, will serve as acting director until a new head of the agency is named.

The email from Stempfley said, "we are confident that our organization will continue its strong performance under his leadership."