South Korean Prime Minister Han Seung-soo visited a set of islets Tuesday at the center of a territorial dispute with Japan as the highest-level official ever to travel there.

Tokyo criticized Han’s brief trip to the rocky outcroppings lying about halfway between the Korean peninsula and Japan.

“I don’t think taking an action like this to highlight our differences is appropriate,” said Japan’s Chief Cabinet Secretary Nobutaka Machimura. “We think it is important to deal with the matter calmly.”

Han, accompanied by culture and transportation ministers, flew to the islets by helicopter and stayed there for about an hour, his office said.

The South Korean-controlled islets, called Dokdo in Korean and Takeshima in Japanese, have long been a source of discord between Seoul and its former colonial ruler Tokyo.

Han’s trip to the islets came as the territorial row flared anew earlier this month when Japan said it would recommend in a government teaching manual that students learn about Tokyo’s claims to the islets.

South Korea recalled its ambassador from Japan in protest and demonstrators have held regular rallies at the Japanese Embassy in Seoul, which has been surrounded by patrols of riot police.

Many in Korea feel bitterness toward Japan because of Tokyo’s 1910-45 colonial rule of the Korean peninsula.

The trip also comes amid anger in South Korea over a U.S. agency’s move to change the status of the islets to “nondesignated sovereignty” on its Web site.

The U.S. Board of Geographical Naming had previously labeled the disputed islets as South Korean territory.

In Washington, State Department spokesman Gonzalo Gallegos said Monday the change does not represent a shift in U.S. policy, saying “we do not take a position on Korea’s claim or Japan’s claim to the islands.”

Meanwhile, South Korea plans to hold an annual naval drill near the islets Wednesday.

The drill, including two F-15 fighter jets and eight vessels, is aimed at reaffirming “our military’s commitment to defend Dokdo and checking the defense posture of Dokdo,” the navy said in a statement.

North Korea condemned Japan on Tuesday for laying claim to the islets, accusing Tokyo of attempting to “grab (Dokdo) at present and the whole of Korea in the future and, furthermore, reinvade the rest of Asia.”

“The Japanese authorities had better stop at once” their attempts to grab the islets, the North’s History Society said in a statement, carried by the North’s official Korean Central News Agency.