South Korean President Lee Myung-Bak said Monday his unprecedented visit to islands claimed by Japan was intended to press Tokyo to settle grievances left over from its colonial rule.
The visit on Friday last week to the Seoul-controlled islands in the Sea of Japan (East Sea) infuriated Japan, which recalled its ambassador from Seoul.
It was the first trip by a South Korean president to the volcanic outcrops known as Dokdo in Korea and Takeshima in Japan. In Tokyo, Prime Minister Yoshihiko Noda called the visit "extremely deplorable".
Lee accused Japan of ignoring demands to resolve issues arising from its harsh 1910-45 rule over Korea, such as women forced into sexual slavery for Japanese troops during World War II.
At last December's summit with Noda, he said, he talked for more than an hour on the issue.
"A powerful nation like Japan can resolve such issues if it decides to do so, but it has shown passive attitudes due to domestic political reasons. So I felt the need to show (Korean grievances) through action," Lee said.
"Japan's influence in the international community isn't as it used to be," he said at a lunch with parliamentary leaders. A presidential spokeswoman confirmed the comments.
Japan and South Korea have close economic ties and shared concerns over North Korea's missile and nuclear programmes. But historical disputes still mar their relationship.
In another assertion of Seoul's sovereignty over the tiny islands, a team of South Koreans Monday began a 230 kilometre (145 mile) relay swim from an eastern port to Dokdo.
The team led by singer Kim Jang-Hoon plans to complete the swim on Liberation Day Wednesday, which marks the ending in 1945 of Japan's colonial rule.
Kim jumped in the sea off Uljin in a full-body swimsuit after a ceremony with about 40 university students and dozens of others, Yonhap news agency reported.
The students, members of a swimming club at the Korea National Sport University, will take part in the 55-hour-long relay led by Kim, it said.
"I will never make such a comment as 'Dokdo is our territory' when I arrive there," Kim told reporters before leaving. "It's meaningless to do so because they are undeniably our territory.