TOKYO (Kyodo) -- Same-sex couples and other plaintiffs in a lawsuit on Japan's ban on same-sex marriage took their case to the Supreme Court on Thursday, appealing a high court ruling last month that recognized the ban as constitutional.

The move came after the Tokyo High Court concluded that the current civil law provisions disallowing same-sex marriage are still reasonable under the current circumstances, making it the only high court ruling to uphold the state's position among six rulings on similar lawsuits filed nationwide.

The Supreme Court is expected to issue a single ruling that applies across all related cases next year at the earliest.

At a press conference in Tokyo, Takako Uesugi, the lawyer representing the eight plaintiffs, criticized the latest ruling, saying it was "extremely different" from the five earlier rulings that deemed the ban incompatible with the Constitution.

"That's something we can never accept," she said about the Nov. 28 ruling, adding, "We will urge the Supreme Court, the guardian of the Constitution, to make a clear decision that the ban is unconstitutional."

Shinya Yamagata, 58, one of the plaintiffs, attended the press conference and expressed hope as the case heads to the Supreme Court.

The Tokyo High Court said that the current marriage system is useful in preparing an environment for raising children, and that it is reasonable to interpret "husband and wife" as a man and a woman.

The court also said that the freedom of marriage guaranteed under Article 24 of the Constitution does not apply to same-sex couples.