France's ambassador to Japan has pledged not to serve under far-right leader Marine Le Pen if she becomes president, saying her policies are at odds with French principles.

Thierry Dana, writing in Le Monde newspaper, became the first high-ranking French diplomat to state publicly that he would step down rather than work for Le Pen if she were to win presidential elections held over two rounds in April and May.

"If the pieces of the French tragedy which are being put in place were to lead to her election, I would stand aside from any diplomatic role," Dana said.