Russia announced on Wednesday that it had arrested a Chinese man for allegedly trying to secure secret documents about its missile systems.
The Federal Security Service said the man, Tun Sheniyun, had been posing as an official interpreter, and was arrested in Moscow on October 28 last year.
His arrest has been kept secret from the media until now, and Agence France-Presse reported that there was no mention of why officials had failed to report the incident.
Tun had allegedly sought technological and repair documentation on the Soviet-era S300 surface-to-air system, reported the BBC.
China is already licensed to manufacture the system, an older version of the S400 now used by Russia.
It is understood that prosecutors on Tuesday forwarded Tun's case to the Moscow City Court.
The FSB said in a statement:
The investigation established that the Chinese national (was) working on assignment from the Ministry of Public Security of the People's Republic of China.
Alongside India, China is one of Russia's largest arms purchasers.