Japan has reportedly protested against a regular military exercise by South Korea near the Dokdo islets.  

According to Japanese public broadcaster NHK, the Japanese foreign ministry announced on Wednesday that it lodged a strong protest with Seoul, calling it unacceptable and extremely regrettable. 

Last week, South Korea conducted a closed-door military exercise aimed at defending East Sea territories near the Doko islets, mobilizing Navy and Coast Guard vessels and Air Force assets.

The military and Coast Guard have carried out the Dokdo defense drills since 1986. From 2003, they've been held twice a year. Japan has strongly protested the drills when they’ve occurred.

Japan's Kyodo News said the South Korean defense ministry has withheld information regarding the drills, apparently to avoid heightening tensions with Japan, which regards the islets as part of its territory and calls them Takeshima.