Chief Cabinet Secretary Katsunobu Kato told reporters Monday that his government is asking Myanmar authorities to explain the arrest and provide other details while asking for his release as soon as possible.
He did not identify the detainee, but Japanese media identified him as Yuki Kitazumi, a former Nikkei business newspaper reporter currently based in Yangon as a freelance journalist.
“We will continue asking the Myanmar side for his early release, while doing our utmost for the protection of the Japanese citizens in that country,” Kato said.
Japan's NHK public television quoted witnesses as saying that they saw Kitazumi being arrested and taken from his home.
Kitazumi had been detained briefly in late February by police while covering pro-democracy protests in Myanmar, where the military ousted the elected government Feb 1.
Japan has stepped up its criticism of Myanmar's deadly crackdown on opposition but has taken a milder approach than the United States and some other countries that imposed sanctions against members of the military junta.
On Saturday, the junta released more than 23,000 prisoners to mark the traditional new year's holiday. At least three had been political prisoners, but it wasn't immediately clear if any activists detained during the post-coup crackdown had been freed.
According to the Assistance Association for Political Prisoners, which monitors casualties and arrests, government forces have killed at least 728 protesters and bystanders since the takeover. The group says 3,141 people, including ousted civilian leader Aung San Suu Kyi are in detention.