Japanese government officials declined to comment Thursday on a reported ransom demand for a Japanese freelance journalist who has been missing since summer in Syria.

The France-based nonprofit group Reporters Without Borders said earlier this week that it had learned that those holding journalist Jumpei Yasuda have started a countdown for a ransom payment, and are threatening to kill him or sell him to another militant group.

Chief Cabinet Secretary Yoshihide Suga told reporters at his daily morning briefing that Japan is doing its utmost to deal with the situation, but he wouldn't confirm any details.

Reporters Without Borders, in a statement posted on its website, is calling on the Japanese government to do everything possible to obtain his release.

Another freelance journalist, Kenji Goto, was among two Japanese killed in Syria by the Islamic State group in January in a hostage crisis that gripped Japan for more than a week. Yasuda went to Syria in part to report on Goto, who was his friend, according to the Reporters Without Borders statement.