SEOUL—Tokyo recalled its ambassador to Seoul on Friday after South Korea President Lee Myung-bak flew to a pair of small islets also claimed by Japan, in a high-profile assertion of territorial rights.

"Dokdo is truly our territory," Mr. Lee said during the visit, the first by a South Korean president to the territory, known as Takeshima in Japan and as Liancourt Rocks by the U.S. and other parties outside the dispute. He added that it is "worth sacrificing our lives over."

Japanese...