The granting of citizenship to a Japanese couple's twins born to a U.S. surrogate mother last fall has been put on hold due to legal obstacles, the couple said Thursday.

The couple, who live in the Kansai region, said the Justice Ministry has yet to accept the notification of the birth of the twin boys on the grounds that it "cannot determine that there is a parent-child relationship" between the couple and the babies. The twins have been living in Japan since spring as U.S. citizens.

Although the government has been promoting legislation for fertility treatment, a health ministry panel in April compiled a final report recommending that surrogate births and the brokering of such births be banned. But experts said loopholes remain in the report, such as the fact that it fails to fully address cases in which the treatment takes place overseas.