Mystery surrounded the disappearance of a Tokyo-based Chinese professor Thursday, amid reports he was being held by Beijing over spying claims.
Colleagues of Zhu Jianrong, 56, professor of international relations in Asia at Toyo Gakuen University, say they are concerned for his safety because they have heard nothing from him since mid July, when he left for his native Shanghai.
"We have no further information and his wife has lost contact with him," a university spokesman told AFP. "We are worried about him."
Zhu, who makes regular appearances on Japanese TV, is under investigation by the Chinese ministry of state security, the Sankei Shimbun and Kyodo News have reported, citing unnamed Chinese sources.
China and Japan have a close economic relationship but a prickly diplomatic one.
They are at loggerheads over disputed islands in the East China Sea, and tensions between them have soared over the last year.
Zhu interviewed several military figures during academic research on the Chinese navy earlier this year, sources told Kyodo.
Tabloid magazine Shukan Shincho said Beijing may believe Zhu has been spying for Japan.
Citing an unnamed senior Japanese foreign ministry official and China watchers, the magazine said despite his membership of the Chinese Communist Party and his pro-China commentaries, Zhu has very close ties with Japanese officials.
The academic was summoned by Chinese security as soon as he arrived for a meeting in Shanghai, the magazine said.
"China will likely launch an anti-Japanese campaign, claiming that Japan stole Chinese information" through Zhu, the ministry official was quoted as saying.
Until this week, Beijing had made no official comment about the case.
"Zhu Jianrong is a Chinese citizen," foreign ministry spokesman Hong Lei told a press conference on Wednesday, when asked whether Zhu had been detained. "Chinese citizens should obey the laws of China."
He did not elaborate, nor confirm whether Zhu was being held.
Zhu came to Japan in 1986 and gained a doctoral degree in politics at Gakushuin University in Tokyo. His wife is Japanese.
He left home for Shanghai in mid July, but did not return when he said he would, the university spokesman said, adding his Shanghai-based brother had telephoned Zhu's wife to say he was ill and would be staying on.
"There was information that he was sick, and we were surprised at the comments by China's foreign ministry yesterday," the spokesman said.
Chinese authorities on occasion hold dissidents and others under house arrest or incommunicado for extended periods.
Police in Shanghai have declined to comment on the case. Relatives in the city could not be reached for comment.