Officials in France have issued an international arrest warrant for a Japanese woman accused of keeping her two children from their French father, AFP news agency reports.
The case has revived debate about "parental kidnapping" in Japan, where there is no concept of shared custody.
Vincent Fichot says his wife disappeared from the family home in Tokyo with their two children three years ago.
He has not seen his children since.
France has now issued a warrant over allegations including parental abduction, the AFP news agency reports.
Mr Fichot made international headlines when he staged a three-week hunger strike during the Tokyo Olympics this year to draw attention to the issue.
Japanese law does not include a provision for separated parents to share custody.
Critics accuse the authorities of looking the other way when one parent blocks the other's access to their children. Rights groups estimate that around 150,000 under-18s are forcibly separated from a parent every year in Japan.
The French warrant also accuses Mr Fichot's wife of endangering a minor.
A lawyer for Mr Fichot's wife told AFP: "Divorce proceedings are ongoing. We have no desire to fight outside of court."