South Korean President Roh Moo-hyun has asked Japan to apologise and consider paying compensation for its colonising of the Korean peninsula last century.
President Roh said ties could not improve without an apology
Japan has expressed regret for its actions before and during World War II, but Mr Roh said Japan should make a formal apology.
"South Korea and Japan should be reborn as good neighbours," Mr Roh said.
Ties between the countries have warmed in recent years, but a new row over disputed islands has stirred tensions.
"Japan must make the truth of the past known and offer sincere apologies and, if necessary, pay compensation. Only then can we be reconciled," said Mr Roh in a speech to mark the anniversary of a 1919 uprising against Japanese colonialists.
"Japan should take a more positive attitude with a belief that before it is a legal issue, this is an issue of universal ethics in a human society and a matter of trust between neighbours," he said, indicating that Tokyo should follow the example of Germany.
The Japanese government argues that any reparations were dealt with under post-war peace treaties.
Japan colonised the Korean peninsula 1910-45
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But newly released details of those treaties have only enraged South Korean public opinion further.
In January, Seoul declassified documents revealing that South Korea's post-war government agreed to accept an $800m economic package as reparations from Japan when the two countries established diplomatic ties in 1965.
Two other issues continue to dog reconciliation efforts. Groups of South Korean women are still seeking compensation from Japan for being forced to work in Japanese brothels before and during the war, and disputed territory is also a sensitive issue.
Anger flared after Japanese ambassador to Seoul, Toshiyuki Takano, said last week that the Dokdo islets in the Sea of Japan (East Sea) - known as Takeshima in Japan - "historically and legally" belong to Japan.
Despite the historic sores, relations have slowly been improving between the two nations in recent years.
In 2002, South Korea and Japan jointly hosted the World Cup, and cultural ties are also increasing - a South Korean soap opera called The Winter Sonata has many avid fans in Japan.