Crown Prince Naruhito may visit France with Crown Princess Masako in September to mark the 160th anniversary of Japan-France diplomatic relations, Imperial Household Agency sources said Thursday.

The crown princess, who has long battled a stress-related illness, has not accompanied her husband on an overseas visit since July 2015 when they visited the South Pacific kingdom of Tonga for a coronation event.

The agency is currently arranging the crown prince's official visit to France in mid-September, according to the sources. He is expected to meet with French President Emmanuel Macron and attend events to introduce Japanese culture.

The crown prince is set to ascend the throne on May 1 next year, taking over from Emperor Akihito who will step down in what will be the first such abdication in the country in about two centuries, while the crown princess -- the Harvard- and Oxford-educated former diplomat -- will become the empress.

She has shown signs of recovery in recent years and has appeared in public more frequently.

Whether the couple will travel together to France is likely to be decided at the last minute, but a senior official of the agency said, "We hope she will feel more confident about herself by making an overseas visit before becoming the empress."

This year marks the 160th anniversary of the establishment of bilateral diplomatic relations between Japan and France. A series of Japanese cultural events called "Japonismes 2018" will be held in Paris and elsewhere from July.