The Chinese man was stopped at the John F. Kennedy International Airport in August for carrying undeclared cash. Reuters

Yu Long, a Chinese national and a former resident of Connecticut, has been charged with trying to take confidential U.S. military documents to China. The man, who was a former employee of a military contractor, has claimed that he worked on F135 engines used in U.S. fighter jets.

Yu was on his way to China last month from New Jersey's Newark Liberty International Airport when customs officers discovered proprietary documents in his luggage, including equations and test results used to develop titanium for U.S. military aircraft, Reuters reported, adding that Yu was arrested two days later in Ithaca, New York.

Yu, who worked as a senior engineer for a Connecticut defense contractor between 2008 and earlier this year, reportedly said that he had experience in working on the F119 and F135 engines, which are manufactured by Hartford, Connecticut-based United Technologies and used in U.S. military planes.

The United Technologies Research Center, which Yu claimed he had worked for, said in a statement that it was cooperating with authorities.

According to prosecutors, authorities had also stopped Yu at New York City's John F. Kennedy International Airport in August for carrying $10,000 in undeclared cash, along with registration documents for a new Chinese corporation and an application to work for a government aviation research center in China, Reuters reported.

In May, the U.S. justice department had charged five Chinese military officers with stealing sensitive data from the computer systems of six U.S. companies and unions. In turn, China had warned the U.S. of retaliatory measures, and had suspended the China-U.S. Cyber Working Group, citing “lack of sincerity” and “deliberately fabricated facts” by the U.S.