Cho June-hyuck, foreign ministry spokesman, told a regular press briefing that Japan did protest the maritime survey with Korea, but the government "dismissed" it.

"Our stance is that we will sternly respond to Japan's unjust claims to our inherent territory," he told reporters. "There is no need for us to ask for prior admission, and we don't have to do such a thing."

Dokdo, a set of rocky islets lying closer to the Korean Peninsula in the East Sea, has long been a recurring source of tension between the neighbors. South Korea has kept a small police detachment on Dokdo since its liberation from Japan in 1945 and has made clear that Tokyo's claims are utterly groundless.

Tensions flared up in 2006 as Japan pushed to conduct its own maritime research near Dokdo in response to South Korea's activities there, but they managed to eschew a clash by agreeing to conduct a joint scientific survey. (Yonhap)