South Korea on Wednesday lodged a protest over Japan's distribution of a Korean-language version of its defense white paper depicting the South Korean islets of Dokdo as Japanese territory, the Yonhap News Agency reported.

"The Seoul government lodged a strong protest against Japan in order to prevent such an unjustifiable act from being repeated," an unidentified South Korean defense ministry official was quoted as saying.

A senior South Korean Defense Ministry official summoned the military attache from the Japanese Embassy in Seoul earlier in the day and handed back copies of the summary.

The attache had delivered 50 of the documents to South Korea's Joint Chiefs of Staff last week, which passed them on to the defense ministry earlier this week.

"We returned the copies when summoning the attache," the official said.

South Korea and Japan are embroiled in a territorial dispute over the islets in the Sea of Japan which Japan calls Takeshima and considers its sovereign territory.