A group of Japanese researchers is pleading for the safe return of a prominent Chinese scholar at Hokkaido University of Education who they have not heard from since shortly after he left for China to attend a family funeral in June.

Friends and colleagues have not been able to get in touch with Yuan Keqin, a professor of East Asian political history, for over six months, according to a statement that was released Tuesday by Hokkaido University professor Akihiro Iwashita and other researchers.

Yuan, who was born in China’s Jilin province in 1955 and studied law at Hitotsubashi University graduate school in Tokyo, is a permanent resident of Japan.

He has not been heard from since July after friends and colleagues learned he was being treated for high blood pressure, Iwashita said.

Hokkaido University of Education said it hopes to get in touch with Yuan soon to confirm how he is doing.

Chinese authorities in September detained Hokkaido University professor Nobu Iwatani for alleged spying. Iwatani, who specialized in studies on the Chinese Nationalist Party during the Second Sino-Japanese War, similar to Yuan’s area of expertise, was released in November.

“We cannot deny the possibility that professor Yuan may be detained as well. If anyone has any information about his safety, please contact me,” Iwashita said.