A policy forum that was supposed to be held in Beijing on Nov. 2 was suspended following China's detention in September of a Japanese professor, a source close to the matter said Wednesday.

After the male professor at Hokkaido University in his 40s was arrested in China for alleged spying, Japanese pundits decided not to visit Beijing, the source said, adding it is uncertain when the forum will take place.

Since 2015, at least 14 Japanese citizens, including the professor, have been detained in China on various charges such as espionage. All of them are civilians, making the latest case involving a national university professor, equivalent to a public servant, the first of its kind.

The policy forum was scheduled to be co-hosted by the Japan Institute of International Affairs, a Tokyo-based think tank, and Peking University in Beijing.

Tokyo and Beijing have agreed to step up coordination for a planned state visit by Chinese President Xi Jinping to Japan next spring, but the detention may blur the outlook for ties between the two countries, which have recently improved, analysts say.

In Japan, a conservative group of the ruling Liberal Democratic Party on Wednesday urged Prime Minister Shinzo Abe's office not to invite Xi to Japan, citing the detention of the professor.

The professor "was detained for unknown reasons and has been deprived of freedom. We cannot say that Japan-China relations have been on a normal track," the group said in a statement.

Ties between Japan and China have often been strained over wartime history and territorial rows, but the two neighbors now describe their relations as having "returned to a normal track."

In a sign of a thaw in bilateral ties, the two nations have promoted reciprocal visits by their leaders. Abe traveled to Beijing in October last year, while Xi paid a visit to Osaka in June to attend the Group of 20 summit and held one-on-one talks with Abe.

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