Japan says it will take a long-running territorial dispute with South Korea to the Hague-based International Court of Justice, after Lee Myung-bak, South Korea's president, made a surprise visit to a group of disputed islands this week.
The islands, known as Takeshima in Japan and Dokdo in South Korea, lie equidistant from the two mainlands and are believed to contain frozen natural gas deposits potentially worth billions of dollars.
"We must consider measures to peacefully resolve the dispute based on international law, including filing a suit with the International Court of Justice," Koichiro Gemba, Japan's foreign minister, announced on Saturday.
However, Japan may find it difficult to bring the matter to the court in The Netherlands, which requires an agreement between the disputing parties to make its ruling binding.
South Korea rejected repeated proposals by Japan in the 1950s and '60s to let the court rule on the issue.
Lee became the first South Korean leader on Friday to make the trip to the islands, which have been a persistent irritant in relations between the two countries.
"We would like to take the step in the not-too-distant future. Until now, the Japanese government has considered what impact such action may have on Japan-South Korea ties," Gemba said.
"But the president's visit to Takeshima made such considerations unnecessary. We must present Japan's position to the international community."
Gemba made the remarks after meeting Japan's ambassador to South Korea, Masatoshi Muto, who was recalled to Tokyo after Lee's trip to the islands, which lie at the centre of a decades-long dispute.
Many Koreans resent Japan's brutal colonisation from 1910 to 1945.
Historical disputes continue to mar their relations, despite close economic ties and shared concerns over North Korea's missile and nuclear programmes.
Lee toured the islands and shook hands with coastguards as a South Korean flag fluttered in the breeze, disregarding Japan's warnings that the visit would strain already prickly relations.
He also travelled 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.
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.
Yoshihiko Noda, Japan's prime minister, said the trip was "extremely deplorable".
Hours after Lee's visit, the glass front door at a South Korean consulate general's office in Hiroshima was shattered by a brick.
Police guarding the building heard the sound of shattering glass around 2:50am local time on Saturday, and saw a motorcycle speed away, national broadcaster NHK said, adding that police suspect it was linked to Lee's trip.