The Tokyo District Court ruled Thursday that the country's nationality law, which forbids citizens from holding multiple nationalities, is constitutional, in a judicial decision believed to be the first concerning the regulation.

In a lawsuit filed with the court, eight men and women in their 30s to 80s, who were born in Japan but now live in Europe, claimed the law's stipulation that Japanese citizens must give up their nationality upon obtaining a foreign nationality violates the Constitution.

But the government argued the plaintiffs' claim took no note of national interest, and that permitting multiple citizenship would allow people to have voting rights or diplomatic protection in other countries.