BEIJING China dismissed accusations it stole F-35 stealth fighter plans as groundless on Monday, after documents leaked by former U.S. intelligence contractor Edward Snowden on a cyber attack were published by a German magazine.
The Pentagon has previously acknowledged that hackers had targeted sensitive data for defense programs such as the F-35 Joint Strike Fighter, but stopped short of publicly blaming China for the F-35 breach.
Defense experts say that China's home-grown stealth jets had design elements resembling the F-35.
The Pentagon and the jet's builder, Lockheed Martin Corp, had said no classified information was taken during the cyber intrusion.
German magazine Der Spiegel on Saturday published a cache of Snowden documents, including a top secret U.S. government presentation that said China stole "many terabytes" of data on the F-35 program, including radar designs and engine schematics.
"The so-called evidence that has been used to launch groundless accusations against China is completely unjustified," Foreign Ministry spokesman Hong Lei told reporters.
Hong said the "complex nature" of cyber attacks makes it difficult to pinpoint the relevant attacker, adding that China wanted to work with other countries to prevent hacking.
"According to the materials presented by the relevant person, some countries themselves have disgraceful records on cyber security," Hong added.
Snowden's 2013 revelations of the broad reach of the National Security Agency's (NSA) spying program sparked international outrage.
Lockheed Martin is producing the F-35 for the U.S. military and allies in a $399 billion project, the world's most expensive weapons program.
It is intended to deliver advanced stealth capabilities, improved manoeuvrability and high-tech sensors, but the program has struggled with delays and budget overruns.
China unveiled its highly anticipated J-31 twin-engine fighter jet at an air show late last year in a show of muscle during a visit to the country by U.S. President Barack Obama.
The aircraft's maker, Aviation Industry Corp of China, caused a stir when its president, Lin Zuoming, said the jet could "take down" the F-35.
President Xi Jinping has pushed to toughen the country's 2.3 million-strong armed forces as China takes a more assertive stance in the region, particularly in the South China and East China seas.
(Reporting by Sui-Lee Wee, Writing by Michael Martina; Editing by Nick Macfie)