"As we have spoken about this issue on many occasions before, we will not respond to the proposal by Japan," the senior diplomat said on the condition of anonymity.
Japanese officials notified the South Korean embassy in Tokyo earlier in the day that Japan's Cabinet was set to endorse the proposal on Friday, the diplomat said, adding that Japanese Foreign Minister Koichiro Gemba will formally deliver the proposal to the Korean Ambassador to Japan Shin Kak-soo later in the day.
It was the first time since 1962 for Japan to make such a proposal to South Korea, the diplomat said.
Japan has considered asking the ICJ to resolve the issue of Dokdo since President Lee Myung-bak made an unprecedented visit to the islets on Aug. 10.
Prospects for taking the issue of Dokdo, which lies closer to South Korea in the body of water between the Korean Peninsula and Japan, to the ICJ are elusive because Tokyo must secure Seoul's consent to have the case heard at the court.
"The government's stance is that there is no territorial dispute over Dokdo because it is clearly a Korean territory historically, geographically and under international law," a senior official at Seoul's foreign ministry said earlier in the day.
"So, we have neither any reason to go the ICJ nor any intention to go there," the official said on the condition of anonymity.
Dokdo has long been a thorn in relations between South Korea and Japan. South Korea keeps a small police detachment on the islets, effectively controlling them.
Japan has long laid claims to Dokdo in school textbooks, government reports and other ways, undercutting better ties between the neighboring nations.
South Koreans see those claims as amounting to denying Korea's rights because the country regained independence from 1910-45 Japanese colonial rule and reclaimed sovereignty over its territory, which includes Dokdo and many other islands around the Korean Peninsula.
The territorial claims have been also viewed by South Koreans as a sign Japan has not fully repented for its imperialist past, along with Tokyo's strict unwillingness to address long-running grievances of elderly Korean women forced into sexual slavery for Japanese troops during World War II.
Related to the diplomatic row with Japan, lawmakers from the ruling Saenuri Party said in a meeting with government policymakers that there is a need to exercise caution when dealing with Dokdo.
"Policymakers should consider warnings that Seoul may be playing into the hands of Tokyo's strategy of trying to show the world that the sovereignty of the islets is in dispute," said Ahn Hong-joon, head of the National Assembly's Unification, Foreign Affairs and Trade Committee.
Rep. Yoo Seong-min and other lawmakers also said that plans to carry out a military drill around the islets should be carefully enforced since it could escalate tensions.
South Korea's military is expected to conduct an exercise early next month around Dokdo that involves deployment of marines as well as the use of warships and fighter aircraft.