The ministry, however, has little means in dealing with the case as Japan is not a party to the 1980 Hague Convention that standardizes laws that prevent international parental child abduction, they said.

Similar cases have been reported in which Japanese women unlawfully take their children to Japan after divorcing or separating from their non-Japanese husbands or partners. Cases in which children are taken out of Japan have been relatively rare.

According to the sources, Kayoko Yamada, a 40-year-old resident of the city of Yamagata, Gifu Prefecture, sought help from the Foreign Ministry after her husband, a 31-year-old Czech Republic national, left home with their son on Aug. 23.

Yamada received a phone call the following day from the husband, saying he and the son were in Frankfurt, Germany.

Yamada has received no contact since then, and assumes that they are probably in the Czech Republic, the sources said.

Yamada and her husband have been living in Japan but recently were talking about divorce.

The Hague Convention stipulates that children should be returned to the original residing place when they are taken forcibly.

Experts say Japan could seek help from Czech authorities in search of the whereabouts of Yamada's son if Japan were a member of the convention.