‘Islets worth sacrificing lives for' – South Korean President South Korean President Lee Myung-bak poses next to a monument which reads,"Korean Territory" as he visits a set of remote islands called Dokdo in Korean and Takeshima in Japanese, east of Seoul, Friday. – Reuters SEOUL – Japan recalled its ambassador to South Korea after South Korean President Lee Myung-bak made a surprise visit Friday to islets at the center of a long-running territorial dispute with Japan, ignoring warnings from Tokyo that it would worsen the neighbors' already strained relations. The disputed islands are believed to contain frozen natural gas deposits potentially worth billions of dollars. Lee is the first South Korean leader to make the trip to the islands that have been a persistent irritant in relations between the two countries even after they moved on from Japan's colonial occupation to develop flourishing commercial ties. Lee placed his hand on a rock carving that says “South Korean territory" during the visit. He also told police officers there that the islets are “worth sacrificing lives for," according to his office. South Korea stations a small contingent of police officers on the disputed islets in a show of control, but Japan maintains that the rocks are its territory. Tokyo renewed the claim last month in an annual defense report. Japanese Prime Minister Yoshihiko Noda told reporters Friday that the islets are “our sovereign territory." “This is completely unacceptable," Noda said. “It is deeply regrettable." He said Japan's ambassador to Seoul was being called back to Tokyo. Japan issued a terse warning over the islands, known as Takeshima in Japanese and Dokdo in Korean, which lie equidistant from the two mainlands, and summoned South Korea's ambassador to Tokyo to formally lodge a complaint. Foreign Minister Koichiro Gemba also said Tokyo had recalled its envoy to Seoul. “The visit to Takeshima by President Lee is unacceptable in light of Japan's stance on this issue," Gemba was quoted as saying by Yonhap news agency. Officials in South Korea said the visit was meant to highlight the islands' importance as a natural reserve and was not aimed at stirring up trouble. “There shouldn't be anything unusual in a national leader visiting a place that is our territory," an official said. Lee traveled to a larger island called Ulleungdo off the Korean peninsula's east coast, which is not disputed, and made the final leg under tight security with military and coast guard escort. Lee's stop on the islands was largely overlooked in South Korea, where he is in the final year of a mandatory single five-year term mired in corruption scandals involving former close aides and family members. – Agencies