Maritime police are on alert for a third day after a group of Japanese right-wing activists announced their plan to land on Dokdo islets.

A Foreign Ministry official said that the four Japanese right-wingers had arrived at Japan's Oki Islands, some 150 kilometers southeast of Dokdo in the East Sea, after departing from Etomo port in Shimane Prefecture on Wednesday afternoon.

The official said that it is uncertain whether the group would make good on their earlier pledge to attempt a landing on the South Korean islets. However, he added that the government is carefully watching the Japanese activists as they are likely to stage a protest of South Korea's claim to the volcanic outcroppings lying half way between the two countries during their stay at Oki.

The members of a right wing group named "Nihon Shidokai" had attempted to sail out for a landing on the South Korean islets earlier on Tuesday but failed due to inclement weather.

Seoul said it will sternly deal with any attempt by the Japanese to land on the islets and threatened to seize their boat and arrest them if they violate South Korea's territorial waters.

The islets have been at the center of a long-running dispute between the two countries. Seoul holds that the islets belong to South Korea, but that Japan began to claim sovereignty over them after it colonized the Korean Peninsula in the early 20th century.