A Japanese citizen has been investigated on suspicion of endangering China's state security, the Foreign Ministry told China Daily on Sunday.

The ministry's spokesperson's office did not elaborate on the identity of the detained Japanese, saying only that the investigation had taken place recently. It said the probe was carried out by government departments, and the Japanese embassy in China had been notified.

Japanese media reported on Thursday that the country's Chief Cabinet Secretary Yoshihide Suga had confirmed that a Japanese man had been detained.

Some Japanese media speculated that the man had been detained on suspicion of espionage.

But Suga denied this at a news conference in Tokyo.

The Tokyo-based Jiji News Agency quoted unnamed sources as saying that the man, aged over 50, had been scheduled to visit China from July 11 to 15.

Japan News Network, a Chinese-language website that reports Japanese news, quoted unnamed sources as saying that the man was a member of the Japan-China Youth Association.

According to the association's website, it is a group that helps to develop friendly relations between the two countries. However, the website is currently not accessible as it is "under maintenance".

Zhou Yongsheng, a professor of Japanese studies at China Foreign Affairs University, said the case may have a negative effect on Chinese public opinion about Japan in the short term.

But he also said it will not deal a major blow to overall Sino-Japanese ties.

"Most of the time, it is no surprise that Tokyo chooses to deny suspected espionage if there are any allegations," Zhou added.