South Korea conducted naval drills in waters near the country's easternmost islets of Dokdo in late June, a government source said Thursday, as Japan continues to lay claims to the rocky outcroppings.

The one-day drill was carried out under a scenario in which other countries approach and illegally land on the islets, the source said. It followed regular maritime drills in the East Sea in the same month.

The source did not say why the drill was not made public at the time.

South Korea has carried out similar military and Coast Guard exercises around Dokdo in previous years in a move seen in part as aimed at bolstering the country's sovereignty over the East Sea islets.

"Under the control of the Joint Chiefs of Staff, the Navy conducted the defense drill in late June," the source said, requesting anonymity. "The drill was carried out under the scenario in which foreign forces landed on Dokdo."

The drill mobilized about 10 ships, including 3,200-ton destroyers and 1,200-ton submarines, as well as the Air Force's F-15K combat jets, the source said.

South Korea has conducted the defense drill once or twice a year in the past and that another drill is scheduled later this year, he added.

Although most exercises in the past had involved the Marine Corps for landing operations, this year's training excluded such maneuvers as it did during the last drill.

Last September, South Korea's Army, Air Force, Navy and Coast Guard attended joint operations in waters near the islets, but landing operations were canceled amid high tensions with Japan after former South Korean President Lee Myung-bak visited Dokdo in August.

Last year, Japan, which has long claimed that Dokdo is its territory, lodged a complaint over the drills through diplomatic channels.

Seoul has rejected Japan's claims as amounting to denying Korea's independence from its 1910-45 colonial rule because Korea reclaimed sovereignty over its territory, including Dokdo and many other islands around the peninsula, when it regained independence from Japan.

South Korea has kept a small police detachment on Dokdo since 1954. (Yonhap News)