The family of a missing French woman is renewing its call for Japan to help gather more information about her on the fifth anniversary of her mysterious disappearance during a trip to a tourist spot north of Tokyo.

"We won't give up. We need answers," Damien Veron, 43, said in a recent interview, referring to his and supporters' efforts to work with Japanese authorities to find out exactly what happened to his sister Tiphaine Veron.

"We would like the existing pieces of evidence to be considered through a criminal investigation," he said.

Damien Veron speaks in an online interview on July 25, 2023. (Kyodo)

Tiphaine went missing on July 29, 2018, when she was 36, after checking in at her accommodation in Nikko, Tochigi Prefecture, the previous day. She left her luggage and passport in her room.

Firmly believing that her disappearance was not an accident but a possible crime amid continuing uncertainties, her family published a book last year titled "Tiphaine Where Are You?" to express their difficulties in dealing with Japan's judicial system.

On Saturday, which marked five years since she went missing, Japanese police handed out flyers in Nikko, asking for information about the woman.

The U.N. Committee on Enforced Disappearances urged Japan to enhance cooperation with French authorities in an April document that said France had opened an investigation of the matter as a kidnapping case.

French authorities asked Japanese police to collect and safeguard relevant mobile phone data in 2018 and 2021, but "received no response," according to the document.

Earlier this month, a top Japanese government spokesman said Tokyo has "properly responded" to the request from the U.N. panel.

"The Tochigi prefectural police have searched for her and taken other actions, suspecting both possibilities -- that she was involved in a crime or an accident," Chief Cabinet Secretary Hirokazu Matsuno told a press conference.

Tiphaine's family "sincerely" thanked the Nikko police for continuing their search for her for five years in a statement released on the fifth anniversary of her disappearance.

It said Tiphaine's case has been handled by an organization for special investigations of old and complex cases in Nanterre, a Paris suburb, and her family will visit Japan in September in a bid to find more clues regarding her fate.

Photo taken July 29, 2023, in Nikko, eastern Japan, shows flyers asking for information on Tiphaine Veron. (Kyodo)