Chinese hackers have gained access to secret designs for a slew of sophisticated U.S. weapons programs, officials said Tuesday, possibly jeopardizing the American military's technological edge.

The breaches were part of a broad Chinese campaign of espionage against top U.S. defense contractors and government agencies, officials said, confirming a Washington Post account of a Pentagon report.

The Defense Science Board, a senior advisory group with government and civilian experts, concluded that digital hackers had gained access to designs for two dozen major weapons systems critical to missile defenses, combat aircraft and naval ships, according to a Pentagon document cited by the Post.

The cyber spying gave China access to advanced technology and could weaken the U.S. military's advantage in the event of a conflict, the board said.

The Pentagon advisory report stopped short of accusing Beijing of stealing the designs, but the conclusions help explain recent American warnings to the Chinese government.

"It's not clear how much of our stuff they got," a defense official told AFP on condition of anonymity.

The revelations of cyber espionage against U.S. contractors coincided with a report that Chinese hackers had stolen top-secret blueprints of Australia's new intelligence agency headquarters, including the layout for communications systems and server locations.

U.S. officials are increasingly worried over digital spying from China and the White House said the issue would be high on the agenda when Chinese President Xi Jinping meets President Barack Obama next week.

"It is an issue that we raise at every level in our meetings with our Chinese counterparts," spokesman Jay Carney told reporters.

"And I'm sure will be a topic of discussion when the president meets with President Xi in California in early June."

The array of weapons designs that were targeted included the advanced Patriot missile system, a U.S. Army program for shooting down ballistic missiles, and the Navy's Aegis missile defense system.

Designs for combat aircraft and ships, including the stealthy new F-35 fighter, the F/A-18 warplane, the V-22 tilt-rotor Osprey, the Black Hawk helicopter and the Navy's new Littoral Combat Ship, were also targeted.

The weapons programs affected are built by major defense contractors including Boeing, Lockheed Martin, Northrop Grumman and Raytheon.

Northrop Grumman spokesman Randy Belote said "the number of attempts to breach our networks are increasing at an alarming rate."

The list of hacked U.S. weapons programs was outlined in a previously undisclosed section of the earlier report by the Defense Science Board.

A public version of the report had warned that America was ill-prepared in the case of a full-scale cyber war.

The Pentagon said in a statement that the department had "growing concerns" about cyber spying, which posed a threat to "the competitive edge of U.S. businesses like those in the Defense Industrial base."

A cyber security expert and former senior U.S. official, James Lewis, said if the report is accurate, "it means the U.S. military is less effective and the Chinese military is more effective."

"It tilts the balance."

He said it was not clear when the breaches took place, but noted that "people did wake up to this issue in the last couple of years and made it harder."

Before that, "between 1999 and 2009 it was an open door for Chinese (cyber) espionage," said Lewis, a fellow at the Center for Strategic and International Studies, a Washington think tank.

But Pentagon spokesman George Little played down the report and said the department had taken steps to bolster cyber defenses and to help contractors counter digital intrusions.

"We maintain full confidence in our weapons platforms," Little said.

"Suggestions that cyber intrusions have somehow led to the erosion of our capabilities or technological edge are incorrect." (AFP)