Figure 1In this Aug. 25, 2019, file photo, service members carry out a military drill on South Korea's easternmost islets of Dokdo in the East Sea to deter trespassers. Yonhap

South Korea conducted regular military drills earlier this week to enhance the defense of its easternmost islets of Dokdo, an informed source said Friday, following Japan's renewed claims to the East Sea outcroppings in a revised security document.

Personnel of the Navy and Coast Guard staged the biannual drills Thursday morning after Tokyo renewed its claims to Dokdo in the revised National Security Strategy last week despite the growing need for bilateral cooperation against evolving North Korean military threats.

The closed-door drills, formally known as the East Sea territory protection training, were aimed at ensuring the country's military readiness to fend off potential foreign infiltrations to the rocky outcroppings, according to the source.

"It is a regular training that our military carries out each year to respond to potential threats to our territory and citizens' property," a Seoul official said on condition of anonymity.

He refused to elaborate on such details as what military assets were deployed to the drills.

South Korea launched the Dokdo drills in 1986. Since 2003, it has conducted them twice a year.

Dokdo has long been a recurring source of tension between the two neighbors, as Tokyo continues to make sovereignty claims in its policy papers, public statements and school textbooks.

South Korea has been in effective control of Dokdo, with a small police detachment, since its liberation from Japan's 1910-45 colonial rule. (Yonhap)