A former senior U.S. government official has criticized Prime Minister Shinzo Abe and other leaders for their historical views toward other parts of Asia during the war.

Jeffrey Bader, former senior adviser for Asian affairs at the National Security Council, also warned Wednesday that the United States could become more "vocal" if Japan reviews past statements in which it formally apologized for its wartime aggression in other parts of Asia.

"The handling of historical issues in the last couple of months by Japanese leaders has not been adroit, to put it mildly," Bader, who assumed the post during President Barack Obama's first term, told a Washington symposium.

He also cited Abe's controversial remark earlier this year that the word "invasion" has no established definition in the context of Japan's militarism and colonial rule over its neighbors in the last century.

Bader also blasted Osaka Mayor Toru Hashimoto for arguing Japan's wartime system of sexual servitude was necessary, branding the remark "crazy."

If Japan adheres to the 1993 apology by Chief Cabinet Secretary Yohei Kono and a 1995 statement expressing remorse by Prime Minister Tomoiichi Murayama, things should be fine, Bader said.