Japan's lack of sincerity in resolving colonial-era issues is the major reason why grievances between the two countries have not been resolved, Yonhap News Agency on Monday quoted Republic of Korea President Lee Myung-bak as saying.

South Korean President Lee Myung-Bak (C) visits a set of remote islands called Dokdo in Korean and Takeshima in Japanese, east of Seoul August 10, 2012. Lee visited the islands on Friday, angering neighbour Japan which also lays claims to territory. South Korea controls the islands with a coast guard presence and plans to beef up maritime research. Lee's scheduled 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.[Photo/Agencies]

According to Yonhap, Lee made the remarks on August 10 while visiting islets that are disputed with Japan.

During his visit to the islets of Dokdo, known as Takeshima in Japan, Lee strongly criticized Japan for not doing enough to soothe the bitter feelings Korean people harbor over colonial rule, Yonhap News Agency said in a report on its website.

"I have no intention of provoking Japan or creating a standoff, but Japan has been too insincere about the issues" related to colonial rule, Lee was quoted as saying.

"Japan should sincerely apologize, but it has not done so."

The agency cited analysis saying that Lee attempted to show the ROK's sovereignty over the islets to Japan, which also claims the islets.

Lee knew that his trip would create dissatisfaction in Japan, but he appears to have determined that it was time to take action, a senior presidential aide told Yonhap.

Harsh Japanese colonial rule left deep scars on the hearts of Korean people. Koreans were banned from using their own language at schools and were forced to adopt Japanese names.

Hundreds of thousands of Koreans were mobilized as forced laborers and also as sex slaves, euphemistically called "comfort women".

Unless it is dealt with as quickly as possible, the sexual slavery issue will remain unresolved forever because elderly comfort women will pass away, Lee said.

The disputes over the Dokdo or Takeshima islets are challenging Seoul-Tokyo ties.

A set of remote islands called Dokdo in Korean and Takeshima in Japanese is seen in this picture taken from a helicopter carrying South Korean President Lee Myung-bak (not pictured), east of Seoul August 10, 2012. [Photo/Agencies]