Prime Minister Shinzo Abe has offered condolences for Americans who died in World War II, as he became the first Japanese leader to address a joint meeting of Congress.

He described reflecting upon the 400,000 American dead from the conflict "with deep repentance in my heart", as he visited the World War II memorial on the National Mall in Washington DC.

"My dear friends, on behalf of Japan and the Japanese people, I offer with profound respect my eternal condolences to the souls of all American people that were lost during World War II," said Mr Abe.

But Mr Abe also acknowledged that Japan's "actions brought suffering to the peoples in Asian countries", but did not go as far as apologising for his nation's wartime conduct.

South Korea has long sought such an apology from Tokyo over the sexual enslavement of tens of thousands of Asian women by Japan's imperial army.