Internal information from the Air Self-Defense Force, including a photo of a model of what is likely a missile currently under development, has been posted on social media, ASDF officials said Thursday.
The ASDF is currently investigating whether any of its personnel were involved, the officials said.
The social media posts have been removed, and the information posted online is not confidential, according to the ASDF.
"The ASDF's information being spread in an inappropriate manner is extremely regrettable and we will respond strictly," ASDF Chief of Staff Gen. Hiroaki Uchikura said at a news conference.
"While we have educated our members on social media use, we need to offer education content that is easy to understand and detailed," he said.
The photo of the missile model was believed to have been taken at an ASDF base in Kakamigahara, Gifu Prefecture, which houses a unit in charge of developing and testing the ASDF's equipment, according to the ASDF and other sources.
The social media posts also mentioned existing equipment.
While acknowledging that undisclosed information has ended up on social media, the ASDF said that there have been no leaks in defense secrets.
The ASDF is looking into a possible breach in its internal rules on using privately owned devices.
The Self-Defense Forces have been under fire for mishandling defense secrets, including on a destroyer. The Defense Ministry is expected to announce punishments over the matter as early as Friday.