US Secretary of State John Kerry extolled the virtues of reconciling with former enemies on Friday as he marked the 20th anniversary of diplomatic relations between the United States and Vietnam.

Wrapping up a five-nation tour of the Middle East and Southeast Asia that has been dogged by domestic US debate over the Iran nuclear deal, Kerry said the Vietnam War was the result of a "most profound failure of diplomatic insight and political vision".

He lamented that current discussions have often focused on the alleged necessity of conflict.