In a sign of the difficulties this nation still faces in holding a healthy debate about the repugnant periods of its history, the prime minister’s statement on the colonial era drew sharp criticism from conservatives. Tabloid newspapers blasted the apology as “treasonous diplomacy,” while right-wing groups loudly protested in front of the prime minister’s residence in central Tokyo.

In Tuesday’s statement, Mr. Kan offered to return historical documents and other cultural artifacts taken from the Korean Peninsula during Japan’s 1910-45 rule. He said he wanted to address the past to build a more forward-looking relationship with South Korea, a country with which Japan enjoys extensive trade, cultural and political ties and whose music and television programs it avidly consumes.

The statement did not mention North Korea, which was also under Japan’s colonial rule before the division of the peninsula. Tokyo has refused to establish diplomatic ties in part because of the North’s abduction of Japanese citizens three decades ago. Nor did it touch on the delicate issue of individual compensation for South Koreans who were forced to work as manual laborers or sex slaves for the Japanese.

“The Japanese government once again came out with more lip service,” said a statement from a group that supports the so-called comfort women, who were forced to have sex with Japanese soldiers during World War II. The group, the Korean Council for the Women Drafted for Military Sexual Slavery by Japan, said that Tokyo must honor international calls to offer clear-cut apologies and reparations for the women. Japan maintains that all compensation issues were settled under the 1965 treaty that normalized relations between South Korea and Japan.