Hong Kong(CNN) China has strenuously denied it stole designs for America's next generation fighter jet, calling the accusations "baseless."
The Foreign Ministry in Beijing responded Monday to the publication by German magazine Der Spiegel of new documents purportedly from NSA leaker Edward Snowden. The ministry's spokesperson Hong Lei told reporters Monday, that he wondered if his country's accusers could produce any evidence to support their claims.
"Cyber attacks are hard to trace back and are usually committed across borders. This complexity means that it is extremely difficult to identify the source of the attacks."
One document reveals that U.S. authorities believe China stole "many terabytes of data" related to its new state-of-the-art F-35 fighter jet, including detailed engine schematics and radar design.
CNN has not been able to independently confirm the authenticity of the document.
The Chinese are currently designing their own stealth fighter aircraft, the FC-31, which analysts have noted resembles the F-35. According to Reuben F. Johnson, a correspondent for IHS Jane's Defence Weekly, the FC-31 "looks" stealthy and its shape mimics that of the F-35 in some respects, but it's questionable whether it rivals its American counterpart from a performance and technological point of view.
A data breach impacting defense contractor Lockheed Martin, the maker of the F-35, was originally reported in 2009. The company told CNN at the time that to its knowledge, no highly classified information had been accessed. It declined to comment on the latest documents.
READ MORE: how good is China's new 'stealth' fighter?
Der Spiegel released a new trove of leaked top-secret documents on Saturday, it says are from the archive of Snowden, a former contractor for the National Security Agency. He is currently living in Russia and faces charges of espionage in the United States.