The US has admitted that secrets were lost when a spy plane made an emergency landing in China.
The crew of the EP-3E plane attempted to destroy sensitive data and equipment after the plane was damaged in a collision with a Chinese fighter plane.
China has refused to release the damaged aircraft, which landed on Hainan island on April 1, after colliding with a Chinese F-8 fighter jet over the South China Sea.
Rear Admiral Craig Quigley said he felt there was a loss of secret information, but has declined to describe the amount or type of damage done.
The American crew members on board the reconnaissance plane were released 11 days later. US officials debriefed them for two days to glean information about the incident.
The National Security Agency, the government office responsible for collecting electronic intelligence, is conducting a review of the potential damage done by the loss of the top-secret aircraft, said two government officials familiar with the study.
The US has demanded that the plane be returned, but talks with the Chinese over the incident have not resolved the situation.
PA