South Korea on Wednesday rejected Japan's protest over an opposition lawmaker's visit to the country's easternmost islets of Dokdo, saying Tokyo should never lay territorial claims to the East Sea outcroppings.

Japan made the protest after Rep. Hong Suk-joon of the main opposition People Power Party visited Dokdo on Sunday in time for Liberation Day, marking the end of Japan's 1910-45 colonial rule of the Korean Peninsula.

A foreign ministry official in Seoul said the government rebutted Japan's claims.

"Dokdo is clearly our inherent territory historically, geographically and by international law. We cannot accept any unreasonable demand or claims from Japan regarding our territorial sovereignty," the official said.

"In accordance with our position, we dismissed the unreasonable demand and claims Japan has made through diplomatic channels," the official said.

Dokdo has long been a recurring source of tension between the two neighbors, as Tokyo continues to make the 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 colonial rule. (Yonhap)