SEOUL - South Korea's military on Monday held an annual drill in islets disputed with Japan to prevent the possible approach of "external forces" to the pair of rocky outcroppings.

Defense Ministry's vice spokesman Wi Yong-seop told a press briefing that the military launched the one-day drill to defend Dokdo, called Takeshima in Japan, saying that it is an annually-held drill to protect the inherent part of South Korea's territory from external forces.

Bad weather conditions left only Navy forces participating in the drill in the morning, Wi said, adding that the landing exercise of marines in the islets is expected to be restricted due to the weather.

The exercise, which has been held twice a year since 1986, was planned to mobilize five to six destroyers and convoys along with F-15K fighter jets, P-3C patrol airplanes and CH-60 and CH-47 helicopters.

The landing training exercise is scheduled to be conducted by a squad of marines from a UH-60 helicopter in the afternoon.

When South Korea held the first round of drill for this year on May 30, Japan protested against it and claimed its sovereignty over the islets. But the country reportedly had yet to make any protest against the drill.

The islets have been controlled by South Korea since 1950s. Japan has laid territorial claims over the islets lying halfway between the two countries.