SEOUL: A South Korean court on Wednesday refused to review a complaint over the 1965 treaty between Japan and South Korea that Tokyo uses to deny compensation for South Korean victims of World War II-era slavery, a boost to recent efforts by the neighbors to improve bad ties.

Seoul's Constitutional Court said that the accord was never meant to serve as a standard for providing individual compensation.

The court's decision came in response to a complaint filed by a woman who said the treaty blocks her right to seek more compensation because of her late father's wartime slavery. Japan colonised the Korean Peninsula from 1910 to 1945.

The 1965 treaty, which was accompanied by more than $800 million in economic aid and loans from Tokyo to Seoul, came as the South worked to rebuild an economy devastated by the 1950-53 Korean War. The treaty declared all compensation issues between the countries on property, rights and interests as "completely and finally" settled.

Relations between the countries, both democracies and strong US allies, have been bad since the 2012 inauguration of Japanese Prime Minster Shinzo Abe, whose nationalistic stance on Japan's wartime past has worried and angered Seoul.

Although the South Korean court has no binding power on international agreements, Seoul could have been obligated to seek a new deal with Tokyo had the court ruled the treaty unconstitutional, analysts said. The decision, however, won't likely stop lawsuits by South Koreans seeking compensation from Japan's government and businesses.

Differences on Japan's responsibility over Koreans enslaved before and during World War II, including Korean women forced to provide sex to Japanese soldiers at front-line military brothels, have been a major source of friction between Seoul and Tokyo.

During a November summit in Seoul, South Korean President Park Geun-hye and Abe agreed to try to resolve the sex slaves matter.

The Japanese government has never directly compensated South Korean victims of wartime slavery but set up a fund in 1995 to make payments to former military sex slaves from private donations. Japanese leaders have previously apologised over the former sex slaves, but many South Koreans see the statements and past efforts at private compensation as insufficient.

Critics say Japan didn't admit to involvement in the military-run brothels until after the 1965 treaty. South Korean officials have also argued that the treaty covered only economic and property claims between the countries, not war crimes or human rights issues.