Chinese cyber hackers have breached networks containing designs for an array of advanced US weapons programs, from stealthy fighter jets to missile defense systems, officials said Tuesday.

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

The Defense Science Board, a senior advisory group with government and civilian experts, concluded digital hackers managed to gain 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 US military's advantage in the event of a conflict, the report said.

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

Precisely how much sensitive technical information the hackers may have obtained was still uncertain, said a defense official, who spoke on condition of anonymity.

"It's not clear how much of our stuff they got," the official told AFP.

The latest revelations of suspected cyber espionage came before China's President Xi Jinping was due to meet President Barack Obama in California next week.

White House spokesman Jay Carney told reporters on Tuesday cyber security will feature in the leaders' talks.

The list of weapons programs affected were outlined in an undisclosed, secret section of a previously released report by the Defense Science Board.

The designs hacked included the advanced Patriot missile system; a US Army system for shooting down ballistic missiles and the Navy's Aegis ballistic missile defense system.

The cyber spying also targeted 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.

A public version of the report disclosed in January had warned the United States was ill-prepared in the case of a full-scale cyber war.

The Pentagon said on Tuesday the department had "growing concerns" about cyber espionage.

The spying posed "a global threat to economic and national security from persistent cyber intrusions aimed at the theft of intellectual property, trade secrets and commercial data, which threatens the competitive edge of US businesses like those in the Defense Industrial Base," it said in a statement.

If the report is accurate, "it means the US military is less effective and the Chinese military is more effective," said James Lewis, a cybersecurity expert at the Center for Strategic and International Studies.

"It tilts the balance."

Lewis, a former US government official, said it was not clear when these breaches took place, but noted that "people did wake up to this issue in the last couple of years and made it harder."

But he said that "between 1999 and 2009 it was an open door for Chinese (cyber) espionage."

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

Lockheed Martin said in a statement that it "has made significant investments in countering cyber security threats and we remain confident in the integrity of our robust, multi-layered information systems security."