The government said Monday it was closely monitoring reports that a Chinese professor at a Japanese university has been missing since he took a trip home over a year ago.

Fan Yuntao, 61, "has been engaged in teaching at a university in Japan for a long time, and the matter could concern the professor's human rights," top government spokesman Yoshimasa Hayashi said.

"We are closely monitoring (the issue)," he said when asked about reports in Japanese media — citing unnamed diplomatic sources — that Fan had been unreachable since visiting China in February 2023.

The sources said Fan was contacted by Chinese authorities before he disappeared, Kyodo News reported. The Yomiuri Shimbun said they may have questioned him.

Fan's employer, Asia University, said he was "on leave" but declined to comment further, citing privacy issues.

Educated at Kyoto University, Fan is a professor of international law and politics, the university's website says.

The reports come just a month after Japan's Kobe Gakuin University said the whereabouts in China of Hu Shiyun, a literature and linguistics professor, were also unknown.

Beijing has sharpened its focus on its nationals abroad in recent years.

In 2019, Yuan Keqin, a professor at Japan's Hokkaido University of Education, vanished after traveling to China for a family funeral. China's foreign ministry later said he had confessed to spying and was in custody.

And in 2013, Zhu Jianrong, a professor at Tokyo's Toyo Gakuen University, was detained by Chinese authorities on suspicion of illegal intelligence-gathering, also after vanishing on a trip home.