A group of U.S. World War II veterans and their relatives say Prime Minister Shinzo Abe should only be invited to give a speech to Congress if he admits Japan's historical responsibility for its wartime conduct, according to a legislative source.

The group sent a letter to influential lawmakers saying Congress should only allow Abe to speak during his planned visit to Washington this spring if they are assured he will acknowledge his country's past deeds, the source said Tuesday.

The plan was revealed as Abe's remarks and behavior over the interpretation of Japan's wartime aggression are being closely watched ahead of the 70th anniversary of Japan's surrender to U.S.-led Allied forces.