BEIJING -- A Chinese professor who specializes in Japanese affairs appears to have been detained by the Chinese government since late July and is being questioned about his activities in Japan, according to Chinese academics and Japanese news media reports.
The apparent arrest of the professor, Zhu Jianrong, possibly on espionage charges, after he returned to Shanghai from Japan comes as relations between China and Japan have hit their lowest point in decades, and has sent tremors of fear through the small community of Japan experts in China and other academics.
A group of Chinese scholars in Japan, the Society of Chinese Professors in Japan, said Monday that it was almost certain Mr. Zhu was being held and was "currently responding to questioning." The society, which Mr. Zhu helped found, described the professor as "very active" in his role as "a bridge between China and Japan."
The Chinese government declined to confirm the arrest but strongly hinted that he had been taken into custody.
In a statement, the Foreign Ministry said: "Zhu Jianrong is a Chinese citizen. China is a country ruled by law, and will protect the legitimate rights and interests of Chinese citizens. While at the same time, all Chinese citizens should abide by the law."
There were some suggestions that Mr. Zhu met with Chinese military officials this year in connection with his research, and that the Chinese authorities were suspicious of those contacts and his subsequent use of the information.
The Japan Times wrote in a Sept. 29 editorial that China was looking into the meetings and whether they constituted an illegal collection of information.
A professor of international relations in Beijing, who declined to be identified because of the delicacy of the case, said he believed Mr. Zhu had been detained on charges of espionage based on his interviews with Chinese military officials.
The case of Mr. Zhu, who often appeared on Japanese television discussing the soured relations between China and Japan, follows a pattern.
In 2009, a former deputy director of the Institute of Japanese Studies at the Chinese Academy of Sciences, Jin Xide, was imprisoned for 14 years on charges of selling Chinese state secrets to Japan and South Korea, according to the Japan Times.
The newspaper also reported that Su Ling, chief editor of Xinhua Shibao, a Chinese-language newspaper published in Japan, has been missing since he came to Beijing from Japan in May.
The disappearance of Mr. Zhu would further fracture the "quasi-cold-war relationship" between China and Japan, setting off fears among Chinese academics and visitors to Japan that they could be susceptible to similar treatment, said Willy Lam, adjunct professor at the Chinese University of Hong Kong's Center for Chinese Studies.
"These folks are not famous people," said Mr. Lam, who has worked in Japan. "Inevitably it will affect people-to-people exchanges, popular diplomacy and people-level diplomacy between the two countries."
In his appearances on Japanese TV, Mr. Zhu was resolute in defending China's case on the bitter dispute over tiny islands in the East China Sea, known as the Diaoyu islands in China and as the Senkaku islands in Japan.
That dispute involves patrols by naval vessels, as well as air sorties, by both China and Japan. China most recently was reported to have sent a drone over the area.
In his television arguments, Mr. Zhu did not appear to be deferential to the Japanese point of view, said a Japanese academic who declined to be identified.
Mr. Zhu married a Japanese researcher in the 1980s, and moved to Japan in 1986, where he worked at Toyo Gakuen University, not far from Tokyo.
The Society of Chinese Professors expressed concern for Mr. Zhu, saying it hoped he would "return to normal life as soon as possible." The group praised him for trying to improve the relationship between the two countries. Mr. Zhu was chairman of the group for nine years.
The case has also frightened Chinese academics in Japan. A member of the group, contacted by telephone, declined to discuss the matter.
Reporting was contributed by Martin Fackler in Tokyo and Jonathan Ansfield in California.
This article originally appeared in The New York Times.