Japanese Prime Minister Naoto Kan has offered the latest of several apologies on behalf of his country to South Korea for Japan's colonial rule decades ago.
It is the latest of several apologies from Japan and is part of an effort to strengthen ties between Japan and South Korea.
During Japan's rule over the Korean peninsula from 1910-45 many Koreans were forced to fight as front-line soldiers, work in slave-labour conditions, or serve as prostitutes in brothels operated by the military.
The issue of Japanese wartime aggression against its Asian neighbours is still a sensitive one more than half a century later.
The Kyodo News agency and other media reports said Mr Kan's apology, which was approved by the Japanese Cabinet, was timed to come ahead of South Korea's celebration of its liberation on August 15.
Mr Kan expressed deep regret over the suffering inflicted during its rule, Kyodo said.
The prime minister said he hopes to build stronger relations with Seoul, and Tokyo will also return some Korean artefacts, according to the reports.
Tokyo has repeatedly apologised in the past for aggression against its Asian neighbours. An apology in 1995 marking the 50th anniversary of the end of the Second World War became the government's official stance.