Japan protested Friday over Seoul's issuance of postage stamps bearing the image of a disputed island in the Sea of Japan.
Foreign Minister Yoriko Kawaguchi expressed regret to South Korean Ambassador to Japan Cho Se Hyung, according to a statement released by the ministry. Japan had repeatedly asked South Korea not to release the controversial stamps.
The island, known as Takeshima in Japan and Tok-do in South Korea, is claimed by both countries.
Seoul said it issued 560,000 sets of stamps, with one set consisting of four kinds of stamps featuring the island.
"The government cannot tolerate" the move, Kawaguchi told Cho. "Takeshima belongs to Japan from legal and historical standpoints."
Kawaguchi said the government will notify members of the Universal Postal Union that South Korea's move is against the spirit of the organization. The union is a Bern-based international organization of postal services.
Cho told Kawaguchi that the island belongs to South Korea, and urged Japan to "carefully deal with the matter" so as not to negatively affect bilateral relations.
During a news conference, Chief Cabinet Secretary Yasuo Fukuda expressed regret over South Korea's move.
Posts minister Taro Aso said he is unhappy at the issuance of the stamps. He said he had expected Seoul to "sensibly" deal with the matter.
Earlier in the month, Aso said Japan should retaliate by creating Takeshima stamps.
The island was placed under U.S. control after Japan's defeat in World War II. South Korea stationed its guards on the island in 1954, claiming that it belonged to Seoul. Japan and South Korea failed to reach an agreement on the territorial issue when they signed a basic treaty to open diplomatic ties in 1965.